Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric Micropumps

Matej Možek, Borut Pečar, Drago Resnik and Danilo Vrtačnik

### Abstract

Quality control of piezoelectric micropumps is presented through design, fabrication process, operation, and characterization. The presented study resulted in the extraction of a minimal set of monitored parameters, which is a prerequisite for reliable and stable micropump operation. Micropump fabrication process steps, especially bonding process quality, in correlation with quality control of micropump constituent components (housing, elastomer, and piezoelectric actuator) provided an explanation for deterioration of common micropump characteristics, such as flow vs. backpressure, suction pressure, and excitation signal. These characteristics also manifested in deterioration of other important micropump properties, such as self-priming ability, bubble tolerance, long-term stability, heat dissipation, and temperature operating range. Besides air and DI water pumping, chemical compatibility of constituent materials was confirmed during successful long-term testing of micropumps by pumping media with different viscosity and aggressive media with low pH value. The extracted set of parameters defines input control for micropump fabrication process while at the same time establishes safe operating area of fabricated micropumps. The presented set of parameters provides quality control guidelines and enables a direct comparison from pump-to-pump or run-to-run variations and extraction of influencing design or fabrication parameters.

Keywords: microcylinder pump, self-priming, bubble tolerance, PZT actuator

#### 1. Introduction

Micropumps are essential components of microfluidic systems. Due to their small size, energy efficiency, low fabrication cost, high performance, and reliability, they are extensively versatile in vital areas of human activities. Application fields for micropumps span from microprocess engineering, medical applications, and diagnostics, to cooling the electronic devices, microtool lubrication, and beyond. Among those activities, an important segment of use includes controlled flow management of the reagents in microfluidic chips for biomedical applications [1], chemical process engineering [2], biochemistry [3], and pharmacy [4], where they can be employed in the system separately or in an integrated form. In order to fully understand the micropump behavior in various applications, micropump as a whole and its constituent parts (piezoelectric disk, elastomer, interlayer adhesive, and plastic housing) have to be thoroughly characterized by taking into account a wide range of parameters. Deterioration of inherent micropump characteristics, such as flow vs. backpressure, suction pressure, and excitation signal are manifested in deterioration of other important properties of micropumps, such as self-priming ability, bubble tolerance, long-term stability, and temperature operating range. Additionally, the quality of micropump system performance is affected by other factors such as viscosity and pH of pumping media, as well as waveform, amplitude, and frequency of excitation signal. All these factors can be explained by the analysis of physical parameter measurements related to evaluation of individual micropump components. Correlations between abovementioned deterioration origins result in a minimal set of dominant monitored parameters, prerequisite for reliable and stable micropump operation. Extracted parameters define input control for micropump fabrication process, while at the same time establishing safe operating area of fabricated micropumps.

The chapter will briefly present micropump design and operation, followed by the description of above-listed micropump characterization methods, which enable quality control. Beside the typical flow rate and backpressure characteristics of the micropump, influence of properties, such as self-priming, bubble tolerance, pumping media compatibility, long-term stability, and temperature dependencies, has been under investigation, and their impact on overall micropump performances has been evaluated. Characterization methods and protocols were established for each of the abovementioned micropump parameters under investigation. Among them, the most relevant characterized parameters for reliable micropump operation will be defined, and correlations which are leading back to constituting components and correlations among them will be presented. Microsystem interactions through pumping media and excitation signal will be thoroughly analyzed, and a resulting set of input parameters in the fabrication of piezoelectric micropumps will be determined. This set of parameters provides quality control guidelines and enables a direct comparison from pump-to-pump or run-to-run variations and extraction of influencing design or fabrication parameters.

#### 2. Case study: microcylinder pump

An innovative microcylinder pump, developed in our laboratory, was selected for a case study of micropump quality control. Microcylinder pump design does not employ any check valves. Instead, it operates on a principle of active sequential expansion (opening) and compression (closing) of the centrally placed inlet cylindrical rectifying element and outlet throttle rectifying element. The expansion/ compression is performed by an actuated glass membrane that is loosely attached via a resilient elastomer to the top of the supporting glass. Exploded view of a typical thermoplastic (TP) microcylinder pump structure with constituent materials and corresponding bonding processes is shown in Figure 1.

fluid into and out of the pump. The micropump chamber and the microchannel are sealed with a thin glass membrane (Figure 1b) by employing oxygen plasma PDMSglass covalent bonding process. Piezoelectric actuator (Figure 1a) is positioned in the axis of a micropump chamber, coupled rigidly to the micropump membrane through silver-filled epoxy adhesive (EPO-TEK EE129-4, Billerica, MA, USA).

Exploded view of a typical TP microcylinder pump structure with constituent materials (a - Piezoelectric actuator, b - thin glass membrane, c - PDMS elastomer layer with micropump chamber, fluidic microchannel, and rectifying elements, d - supporting TP substrate, e - PDMS fluidic connections) and corresponding bonding

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

DOI: http://dx.doi.org/10.5772/intechopen.82857

Microcylinder pump operation is depicted in Figure 2, which is showing (a) the micropump with no excitation signal applied and two distinctive operation cycle phases, (b) pumping phase and (c) suction phase. During excitation, loosely attached glass membrane and PDMS elastomer layer deform in a controlled manner, which enables compression and expansion of the centrally placed inlet cylindrical port, micropump chamber, and outlet throttle shaped port with a specific

phase lag, contributing to efficient micropump operation.

Figure 1.

97

processes (dimensions are not to scale).

The TP microcylinder pump comprises polydimethylsiloxane (PDMS) elastomer layer with molded micropump chamber, fluidic microchannel, and rectifying elements (Figure 1c). Additionally, two through-holes are punched into an elastomer, one into the center of the micropump chamber and the other one at the end of the channel. PDMS elastomer layer (Figure 1c) and PDMS fluidic connections (Figure 1e) are covalently bonded to the supporting TP substrate (Figure 1d) by employing developed amine-PDMS linker bonding process. One inlet and one outlet fluid port is drilled through a supporting TP substrate that supply and drain the

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

#### Figure 1.

understand the micropump behavior in various applications, micropump as a whole and its constituent parts (piezoelectric disk, elastomer, interlayer adhesive, and plastic housing) have to be thoroughly characterized by taking into account a wide range of parameters. Deterioration of inherent micropump characteristics, such as flow vs. backpressure, suction pressure, and excitation signal are manifested in deterioration of other important properties of micropumps, such as self-priming ability, bubble tolerance, long-term stability, and temperature operating range. Additionally, the quality of micropump system performance is affected by other factors such as viscosity and pH of pumping media, as well as waveform, amplitude, and frequency of excitation signal. All these factors can be explained by the analysis of physical parameter measurements related to evaluation of individual micropump components. Correlations between abovementioned deterioration origins result in a minimal set of dominant monitored parameters, prerequisite for reliable and stable micropump operation. Extracted parameters define input control for micropump fabrication process, while at the same time establishing safe operating area of

Quality Management and Quality Control - New Trends and Developments

The chapter will briefly present micropump design and operation, followed by the description of above-listed micropump characterization methods, which enable quality control. Beside the typical flow rate and backpressure characteristics of the micropump, influence of properties, such as self-priming, bubble tolerance, pumping media compatibility, long-term stability, and temperature dependencies, has been under investigation, and their impact on overall micropump performances has been evaluated. Characterization methods and protocols were established for each of the abovementioned micropump parameters under investigation. Among them, the most relevant characterized parameters for reliable micropump operation will be defined, and correlations which are leading back to constituting components and correlations among them will be presented. Microsystem interactions through pumping media and excitation signal will be thoroughly analyzed, and a resulting set of input parameters in the fabrication of piezoelectric micropumps will be determined. This set of parameters provides quality control guidelines and enables a direct comparison from pump-to-pump or run-to-run variations and extraction of

An innovative microcylinder pump, developed in our laboratory, was selected for a case study of micropump quality control. Microcylinder pump design does not employ any check valves. Instead, it operates on a principle of active sequential expansion (opening) and compression (closing) of the centrally placed inlet cylindrical rectifying element and outlet throttle rectifying element. The expansion/ compression is performed by an actuated glass membrane that is loosely attached via a resilient elastomer to the top of the supporting glass. Exploded view of a typical thermoplastic (TP) microcylinder pump structure with constituent mate-

The TP microcylinder pump comprises polydimethylsiloxane (PDMS) elastomer layer with molded micropump chamber, fluidic microchannel, and rectifying elements (Figure 1c). Additionally, two through-holes are punched into an elastomer, one into the center of the micropump chamber and the other one at the end of the

rials and corresponding bonding processes is shown in Figure 1.

channel. PDMS elastomer layer (Figure 1c) and PDMS fluidic connections (Figure 1e) are covalently bonded to the supporting TP substrate (Figure 1d) by employing developed amine-PDMS linker bonding process. One inlet and one outlet fluid port is drilled through a supporting TP substrate that supply and drain the

fabricated micropumps.

influencing design or fabrication parameters.

2. Case study: microcylinder pump

96

Exploded view of a typical TP microcylinder pump structure with constituent materials (a - Piezoelectric actuator, b - thin glass membrane, c - PDMS elastomer layer with micropump chamber, fluidic microchannel, and rectifying elements, d - supporting TP substrate, e - PDMS fluidic connections) and corresponding bonding processes (dimensions are not to scale).

fluid into and out of the pump. The micropump chamber and the microchannel are sealed with a thin glass membrane (Figure 1b) by employing oxygen plasma PDMSglass covalent bonding process. Piezoelectric actuator (Figure 1a) is positioned in the axis of a micropump chamber, coupled rigidly to the micropump membrane through silver-filled epoxy adhesive (EPO-TEK EE129-4, Billerica, MA, USA).

Microcylinder pump operation is depicted in Figure 2, which is showing (a) the micropump with no excitation signal applied and two distinctive operation cycle phases, (b) pumping phase and (c) suction phase. During excitation, loosely attached glass membrane and PDMS elastomer layer deform in a controlled manner, which enables compression and expansion of the centrally placed inlet cylindrical port, micropump chamber, and outlet throttle shaped port with a specific phase lag, contributing to efficient micropump operation.

#### Figure 2.

Microcylinder pump operation cycle: (a) No excitation signal applied, (b) suction phase (membrane expansion), and (c) pumping phase (membrane compression).

Detailed microcylinder operation and fabrication process is reported elsewhere [5].

#### 3. Fabrication quality control

#### 3.1 Quality control of micropump housing

Micropumps were first developed on flat ABS substrates. In this case, surface flatness of ABS is usually in the range 5–7 μm and does not introduce any notable stress in glass membrane after covalent bonding, which would result in micropump performance deterioration. In a more mature phase of development, efforts were focused toward industrial product. Therefore, ABS housing was developed with corresponding changes to adapt all the previous assembly steps. The influence of specific housing construction and adapted process steps should be therefore carefully evaluated in terms of micropump performances. The flatness of the injection molded ABS housing, which serves as a micropump substrate, was found to be critical, since the PDMS and glass membrane are attached by covalent bonding directly on flat part of ABS housing. Irregular flatness of ABS substrate directly transfers on the membrane via strong chemical bonds and results in a local mechanical stress.

Flatness tolerance below 10 μm was found to accommodate bonded layers, keeping them in low-stress regime, thus, without affecting the pump performance. This measurement with established tolerance was found to be one of the prerequi-

Flatness profiles of (a) irregular surface in the early stage of development causing frequent micropump malfunction and (b) surface that fulfills the tolerance range of micropump performances and reliable operation

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

DOI: http://dx.doi.org/10.5772/intechopen.82857

Covalent bonding of constituent micropump components during fabrication process has many advantages over use of adhesives. Covalent bonding does not introduce any additional materials, which would get in contact with aggressive pumping media. Due to absence of glue, micropump fluidic structures cannot be

sites in a sequence of quality control steps.

(Kolektor Group, Idrija, Slovenia).

Figure 3.

99

3.2 Quality control of micropump bonding process

contaminated or even clogged during fabrication process.

Quality of the surface relief should be closely monitored in the stage of injection molding by adjusting the process parameters. Prior to optimization, the surface topography scans (Figure 3a) showed flatness tolerance around 40 μm with high gradients that resulted in poor yield and low flowrate and backpressure performances. The stress in glass membrane can further affect the pump behavior via severely decreasing the throttle valve gap, consequently causing spontaneous sticking of PDMS and glass and ultimately a malfunction.

After adjusting the injection molding process parameters, we were able to achieve flatness comparable with flat substrates and were below 10 μm across <sup>2</sup> 2 cm2 area of the housing size, which is shown in Figure 3b.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

#### Figure 3.

Detailed microcylinder operation and fabrication process is reported

Microcylinder pump operation cycle: (a) No excitation signal applied, (b) suction phase (membrane

Quality Management and Quality Control - New Trends and Developments

Micropumps were first developed on flat ABS substrates. In this case, surface flatness of ABS is usually in the range 5–7 μm and does not introduce any notable stress in glass membrane after covalent bonding, which would result in micropump performance deterioration. In a more mature phase of development, efforts were focused toward industrial product. Therefore, ABS housing was developed with corresponding changes to adapt all the previous assembly steps. The influence of specific housing construction and adapted process steps should be therefore carefully evaluated in terms of micropump performances. The flatness of the injection molded ABS housing, which serves as a micropump substrate, was found to be critical, since the PDMS and glass membrane are attached by covalent bonding directly on flat part of ABS housing. Irregular flatness of ABS substrate directly transfers on the mem-

brane via strong chemical bonds and results in a local mechanical stress.

ing of PDMS and glass and ultimately a malfunction.

<sup>2</sup> 2 cm2 area of the housing size, which is shown in Figure 3b.

Quality of the surface relief should be closely monitored in the stage of injection molding by adjusting the process parameters. Prior to optimization, the surface topography scans (Figure 3a) showed flatness tolerance around 40 μm with high gradients that resulted in poor yield and low flowrate and backpressure performances. The stress in glass membrane can further affect the pump behavior via severely decreasing the throttle valve gap, consequently causing spontaneous stick-

After adjusting the injection molding process parameters, we were able to achieve flatness comparable with flat substrates and were below 10 μm across

elsewhere [5].

Figure 2.

98

3. Fabrication quality control

3.1 Quality control of micropump housing

expansion), and (c) pumping phase (membrane compression).

Flatness profiles of (a) irregular surface in the early stage of development causing frequent micropump malfunction and (b) surface that fulfills the tolerance range of micropump performances and reliable operation (Kolektor Group, Idrija, Slovenia).

Flatness tolerance below 10 μm was found to accommodate bonded layers, keeping them in low-stress regime, thus, without affecting the pump performance. This measurement with established tolerance was found to be one of the prerequisites in a sequence of quality control steps.

#### 3.2 Quality control of micropump bonding process

Covalent bonding of constituent micropump components during fabrication process has many advantages over use of adhesives. Covalent bonding does not introduce any additional materials, which would get in contact with aggressive pumping media. Due to absence of glue, micropump fluidic structures cannot be contaminated or even clogged during fabrication process.

Many strategies for plastic-PDMS bonding have been reported, such as sol-gel coating approach, chemical gluing approach, and organofunctional silanes approach [6, 7], where thermoplastics in the presence of amine undergo aminolysis followed by chain scission of the carbonyl backbone, forming a strong urethane bond. One of organofunctional silanes is amine-PDMS linker (poly [dimethyl siloxane-co- (3-aminopropyl) methyl siloxane]). Amine-PDMS linker incorporates an amine functionality at one terminal and a segment of low-molecular-weight PDMS at the other, which provide better hydrolytic bond stability over commonly employed organofunctional silane APTES [8].

In our micropump fabrication process, thermoplastic (TP) substrates are cleaned in ultrasonic bath, followed by silylation of the surfaces through the use of amine-PDMS linker. After plasma activation, the activated surfaces of the two substrates are brought into contact, using methanol as an aligning medium. Detailed bonding process procedure was reported elsewhere [9].

It is reasonable to evaluate bond strength by employing effective destructive methods on simple burst pressure test devices rather than on fabricated micropumps. Pressure regulated air supply is connected to the inlet of the test device and the pressure at which the device fails is determined. Burst pressure test devices enable optical observation of bond failure at fluidic channel sharp corners, where the structural stress caused by applied fluidic pressure is the largest. Burst pressure tests should be performed with water and compressed air.

polymerization component ratio, increased Young modulus of elasticity is in agree-

An automated system for micropump characterization was designed. Such system comprises a high voltage waveform generator, which is connected to a PC and a dedicated computer software that automatically drives the micropumps and simultaneously saves measured flowrate or back pressure data. Instantaneous water flowrate can be measured with flow meter or as in our case computed by gravimetric method (Q = dm/dt ρ), employing a precision scale connected to a PC. If gravimetric method is used, the water level of collecting tank on the scale should be matched with water level of storage tank by placing the tank on laboratory elevator. To minimize evaporation of water from a surface of an open

collecting tank, the tank can be shaped as a cylinder with a small diameter. Falling droplets can be avoided by pre-filling the collection tank with tare amount of

In our case, excitation signal frequency at constant amplitude or vice versa is swept automatically (0–300 Hz with step of 5 Hz every 10 s and 0–250 V with step of 5 V every 10 s, respectively). Instantaneous air flowrate is measured with Microbridge Mass Airflow Sensor (AWM3150V, Honeywell, NJ, USA), while instantaneous backpressure/suction pressure of both water and air is measured with calibrated differential pressure sensor (HCX005D6V, First Sensor AG, Berlin, Germany). Both are connected to PC via digital multimeter Keithley 2700 (Keithley

First, frequency sweeps are performed up to 300 Hz at maximum admissible

amplitude in order to determine optimal performance frequency for a given pumping medium. After the optimal frequency is evaluated, the amplitude sweeps are performed up to maximum admissible value at optimal excitation frequency. In both measuring procedures, flowrate or backpressure/suction pressure data are simultaneously acquired. An example of measured performance characteristics is

4. Essential micropump measurements for quality control

Micropump flow rate and backpressure performance vs. curing temperature of PDMS polymer.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

ment with reduced DI flow rate.

DOI: http://dx.doi.org/10.5772/intechopen.82857

water.

Figure 4.

instruments, OH, USA).

shown in Figure 5 [5].

101

Our burst pressure tests confirmed hydrolytic stability of TP-PDMS bonds established through amine-PDMS linker [9]. It is speculated that the waterrepelling nature of the PDMS component in amine-PDMS linker prevents penetration of the aqueous solutions at the interface improving bond hydrolytic resistance [10, 11].

#### 3.3 Elastomer mechanical properties control

Mechanical properties of viscoelastic PDMS material, which is one of the crucial parts of here discussed micropump, are mainly influenced by mixing ratio, curing temperature process, and additional aging at moderate temperatures to stabilize the polymer. It is therefore mandatory to determine the appropriate parameters in the preparation phase that can later affect the micropump operation.

According to our measurements and evaluations performed, micropump flow rate and backpressure performance depend strongly on curing temperature of PDMS polymer as shown in Figure 4.

In this particular experiment, four microcylinder pumps were fabricated differing only in PDMS elastomer curing temperature setting during fabrication process. First sample underwent our standard curing temperature of 80°C, and three others underwent curing temperatures of 110, 150, and 200°C. Curing time at all selected curing temperatures was set to 2 hours. After the micropumps were assembled, they were additionally exposed to a setting temperature of 80°C for 14 hours. This process step is a standard step in our well-established micropump fabrication process and was initially introduced in order to stabilize covalent bonds between constituent materials.

It was shown that DI flow rate can be reduced by more than 50%, if curing temperature is increased from 80 to 200°C. Correspondingly, Young modulus of elasticity (E) from the literature [12] increases by 61% in this temperature range. Increased PDMS curing temperature reflects in greater stiffness of elastomer layer, which impairs the magnitude of membrane deformation, pumping stroke volume, and rectifying elements efficiency. By taking into account the same base to

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

Figure 4. Micropump flow rate and backpressure performance vs. curing temperature of PDMS polymer.

polymerization component ratio, increased Young modulus of elasticity is in agreement with reduced DI flow rate.

#### 4. Essential micropump measurements for quality control

An automated system for micropump characterization was designed. Such system comprises a high voltage waveform generator, which is connected to a PC and a dedicated computer software that automatically drives the micropumps and simultaneously saves measured flowrate or back pressure data. Instantaneous water flowrate can be measured with flow meter or as in our case computed by gravimetric method (Q = dm/dt ρ), employing a precision scale connected to a PC. If gravimetric method is used, the water level of collecting tank on the scale should be matched with water level of storage tank by placing the tank on laboratory elevator. To minimize evaporation of water from a surface of an open collecting tank, the tank can be shaped as a cylinder with a small diameter. Falling droplets can be avoided by pre-filling the collection tank with tare amount of water.

In our case, excitation signal frequency at constant amplitude or vice versa is swept automatically (0–300 Hz with step of 5 Hz every 10 s and 0–250 V with step of 5 V every 10 s, respectively). Instantaneous air flowrate is measured with Microbridge Mass Airflow Sensor (AWM3150V, Honeywell, NJ, USA), while instantaneous backpressure/suction pressure of both water and air is measured with calibrated differential pressure sensor (HCX005D6V, First Sensor AG, Berlin, Germany). Both are connected to PC via digital multimeter Keithley 2700 (Keithley instruments, OH, USA).

First, frequency sweeps are performed up to 300 Hz at maximum admissible amplitude in order to determine optimal performance frequency for a given pumping medium. After the optimal frequency is evaluated, the amplitude sweeps are performed up to maximum admissible value at optimal excitation frequency. In both measuring procedures, flowrate or backpressure/suction pressure data are simultaneously acquired. An example of measured performance characteristics is shown in Figure 5 [5].

Many strategies for plastic-PDMS bonding have been reported, such as sol-gel coating approach, chemical gluing approach, and organofunctional silanes approach [6, 7], where thermoplastics in the presence of amine undergo aminolysis followed by chain scission of the carbonyl backbone, forming a strong urethane bond. One of organofunctional silanes is amine-PDMS linker (poly [dimethyl siloxane-co- (3-aminopropyl) methyl siloxane]). Amine-PDMS linker incorporates an amine functionality at one terminal and a segment of low-molecular-weight PDMS at the other, which provide better hydrolytic bond stability over commonly employed

Quality Management and Quality Control - New Trends and Developments

In our micropump fabrication process, thermoplastic (TP) substrates are cleaned in ultrasonic bath, followed by silylation of the surfaces through the use of amine-PDMS linker. After plasma activation, the activated surfaces of the two substrates are brought into contact, using methanol as an aligning medium. Detailed

It is reasonable to evaluate bond strength by employing effective destructive

Our burst pressure tests confirmed hydrolytic stability of TP-PDMS bonds established through amine-PDMS linker [9]. It is speculated that the waterrepelling nature of the PDMS component in amine-PDMS linker prevents penetration of the aqueous solutions at the interface improving bond hydrolytic resis-

Mechanical properties of viscoelastic PDMS material, which is one of the crucial parts of here discussed micropump, are mainly influenced by mixing ratio, curing temperature process, and additional aging at moderate temperatures to stabilize the polymer. It is therefore mandatory to determine the appropriate parameters in the

According to our measurements and evaluations performed, micropump flow rate and backpressure performance depend strongly on curing temperature of

In this particular experiment, four microcylinder pumps were fabricated differing only in PDMS elastomer curing temperature setting during fabrication process. First sample underwent our standard curing temperature of 80°C, and three others underwent curing temperatures of 110, 150, and 200°C. Curing time at all selected curing temperatures was set to 2 hours. After the micropumps were assembled, they were additionally exposed to a setting temperature of 80°C for 14 hours. This process step is a standard step in our well-established micropump fabrication process and was initially introduced in order to stabilize covalent bonds between constituent materials. It was shown that DI flow rate can be reduced by more than 50%, if curing temperature is increased from 80 to 200°C. Correspondingly, Young modulus of elasticity (E) from the literature [12] increases by 61% in this temperature range. Increased PDMS curing temperature reflects in greater stiffness of elastomer layer, which impairs the magnitude of membrane deformation, pumping stroke volume, and rectifying elements efficiency. By taking into account the same base to

methods on simple burst pressure test devices rather than on fabricated micropumps. Pressure regulated air supply is connected to the inlet of the test device and the pressure at which the device fails is determined. Burst pressure test devices enable optical observation of bond failure at fluidic channel sharp corners, where the structural stress caused by applied fluidic pressure is the largest. Burst

pressure tests should be performed with water and compressed air.

preparation phase that can later affect the micropump operation.

organofunctional silane APTES [8].

tance [10, 11].

100

bonding process procedure was reported elsewhere [9].

3.3 Elastomer mechanical properties control

PDMS polymer as shown in Figure 4.

Figure 5. Flow rate, backpressure, and suction pressure vs. excitation signal frequency and excitation signal amplitude characteristics for DI water and air.

for 140 minutes in total. In between, the samples were repeatedly disconnected, clamped into d33 piezometer, measured, and then connected again to the driver. To minimize measurement error, samples were always clamped on the same central spot. Figure 6 shows measured d33 modulus vs. number of switching cycles for two commercially available PZT samples for two applied waveforms with a frequency of 100 Hz and with an excitation amplitude of 120 V. For both PZT samples, d33 modulus decreased mainly in the first 10<sup>5</sup> switching cycles (21% for manufacturer nr. 1 and 19% for manufacturer nr. 2), after that the downward trend was signif-

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

As expected, d33 modulus stability was affected also by excitation signal shape. In our case, square excitation waveform yielded greater decline (+9.3% for manufacturer nr.1 sample and + 6.3% for manufacturer nr. 2 sample) in d33 modulus in

Next, d33 modulus stability was investigated regarding the amplitude of applied excitation signal. Before each d33 measurement, samples were driven with square excitation waveform for 10 seconds at preselected excitation signal amplitude values. Measurements on samples after initial operation by applying electric field yielded higher d33 values compared to measured off-the-shelf d33 values. It is also known from the literature that after poling step, the material microstructure tends to relax the in logarithmical manner, thus decreasing the

After gradual incensement of excitation signal amplitude, d33 modulus decreased

Regarding micropump operation, PZT fatigue effect is the most evident when measuring the dependency of flow rate vs. applied voltage on PZT. This is the property that deserves close attention when setting the safety margins (safe

at a rate of 0.445 pC/NV and 1.2 pC/NV for manufacturer nr. 1 and nr. 2, respectively. Although manufacturer nr. 2 sample yielded higher initial d33 values compared to manufacturer nr. 1 sample, both performed equally at excitation signal amplitude of 160 V. However, manufacturer nr. 2 sample failed permanently at 180 V. Next, d33 modulus stability was investigated regarding the amplitude of

first 10<sup>5</sup> switching cycles compared to custom driver waveform.

icantly reduced.

Figure 6.

PZT d33 modulus stability vs. switching cycles.

DOI: http://dx.doi.org/10.5772/intechopen.82857

initial d33.

103

applied excitation signal (Figure 7).

#### 5. Additional parameters for assessing pump quality

#### 5.1 Quality control of PZT actuator

PZT actuator converts one part of electrical energy into mechanical energy needed for micropump operation. Ferroelectric ceramics are subjected to degradation either during electrical loading (fatigue) or with time in the absence of an external mechanical or electrical load (aging) [13].

To assess the stability of piezoelectric actuator, piezoelectric d33 modulus measurements were performed first on unattached piezoelectric actuators using d33 piezometer PM10 (@100 Hz). Measuring of d33 modulus is fast and easy to perform in opposition with d31 modulus that requires advanced and time-consuming measuring methods. It was assumed that measured d33 modulus and essential d31 modulus that affect micropump operation are proportional to each other. Degradation of d31 modulus is our core concern as it directly affects micropump flowrate and backpressure performance stability.

Piezometer d33 system implements Berlincourt method. After clamping the sample and subjecting it to a low frequency force, the system processes the electrical signals from the sample, compares it with a built-in reference, and calculates d33 modulus. Modulus d33 implies an induced strain in direction of PZT disc rotation axis per unit electric field applied in the same direction.

First, d33 modulus stability over time was evaluated by applying stable square excitation waveform and custom generator waveform on unattached PZT samples Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

Figure 6. PZT d33 modulus stability vs. switching cycles.

for 140 minutes in total. In between, the samples were repeatedly disconnected, clamped into d33 piezometer, measured, and then connected again to the driver. To minimize measurement error, samples were always clamped on the same central spot. Figure 6 shows measured d33 modulus vs. number of switching cycles for two commercially available PZT samples for two applied waveforms with a frequency of 100 Hz and with an excitation amplitude of 120 V. For both PZT samples, d33 modulus decreased mainly in the first 10<sup>5</sup> switching cycles (21% for manufacturer nr. 1 and 19% for manufacturer nr. 2), after that the downward trend was significantly reduced.

As expected, d33 modulus stability was affected also by excitation signal shape. In our case, square excitation waveform yielded greater decline (+9.3% for manufacturer nr.1 sample and + 6.3% for manufacturer nr. 2 sample) in d33 modulus in first 10<sup>5</sup> switching cycles compared to custom driver waveform.

Next, d33 modulus stability was investigated regarding the amplitude of applied excitation signal. Before each d33 measurement, samples were driven with square excitation waveform for 10 seconds at preselected excitation signal amplitude values. Measurements on samples after initial operation by applying electric field yielded higher d33 values compared to measured off-the-shelf d33 values. It is also known from the literature that after poling step, the material microstructure tends to relax the in logarithmical manner, thus decreasing the initial d33.

After gradual incensement of excitation signal amplitude, d33 modulus decreased at a rate of 0.445 pC/NV and 1.2 pC/NV for manufacturer nr. 1 and nr. 2, respectively. Although manufacturer nr. 2 sample yielded higher initial d33 values compared to manufacturer nr. 1 sample, both performed equally at excitation signal amplitude of 160 V. However, manufacturer nr. 2 sample failed permanently at 180 V. Next, d33 modulus stability was investigated regarding the amplitude of applied excitation signal (Figure 7).

Regarding micropump operation, PZT fatigue effect is the most evident when measuring the dependency of flow rate vs. applied voltage on PZT. This is the property that deserves close attention when setting the safety margins (safe

5. Additional parameters for assessing pump quality

Quality Management and Quality Control - New Trends and Developments

external mechanical or electrical load (aging) [13].

axis per unit electric field applied in the same direction.

PZT actuator converts one part of electrical energy into mechanical energy needed for micropump operation. Ferroelectric ceramics are subjected to degradation either during electrical loading (fatigue) or with time in the absence of an

Flow rate, backpressure, and suction pressure vs. excitation signal frequency and excitation signal amplitude

To assess the stability of piezoelectric actuator, piezoelectric d33 modulus measurements were performed first on unattached piezoelectric actuators using d33 piezometer PM10 (@100 Hz). Measuring of d33 modulus is fast and easy to perform in opposition with d31 modulus that requires advanced and time-consuming measuring methods. It was assumed that measured d33 modulus and essential d31 modulus that affect micropump operation are proportional to each other. Degradation of d31 modulus is our core concern as it directly affects micropump flowrate and

Piezometer d33 system implements Berlincourt method. After clamping the sample and subjecting it to a low frequency force, the system processes the electrical signals from the sample, compares it with a built-in reference, and calculates d33 modulus. Modulus d33 implies an induced strain in direction of PZT disc rotation

First, d33 modulus stability over time was evaluated by applying stable square excitation waveform and custom generator waveform on unattached PZT samples

5.1 Quality control of PZT actuator

characteristics for DI water and air.

Figure 5.

102

backpressure performance stability.

Figure 7. PZT d33 modulus stability vs. excitation signal amplitude.

operation area) and is one of quality criteria finally reflected through the pump performance deterioration.

overdriven. Instead, it behaves as shown in Figure 9, and at 140 V, (shown for two distinct manufacturers) one preserved the air flow stability, the other deterio-

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

Constituent materials of the micropump being in direct contact with medium, each having its specific chemical and mechanical properties, should withstand longterm micropump operation without failure. It is therefore mandatory to determine their chemical resistance and fatigue issues. In this respect, a variety of media with distinct pH and different viscosities should also be included in micropump quality control test set. To provide reliable data in the specification list, the micropump tests were performed under continuous operation in the time period between 10 and 300 hours. A set of presented tests, summarized in Table 1, comprised common

> pH (/) Density (g/cm3 )

1 7 1 6 1.62

1 6.5 1 1 1.71

DI water 1 6.5 1 24 1.73 City water 1 7.1 1 24 1.68 Glycol DG372 32 10 1.09 6 0.033

PBS 1.07 7.4 1.06 6 1.61 Sn bath NA 1 1.62 48 0.49 Ni bath NA 4 1.64 90 0.37 1MH2SO4 1.12 1 1.07 136 0.45

Test time (hours)

Flow rate (ml/min)

rated rapidly.

Saline 0.9% NaCl

DI water after tests

Table 1.

105

Figure 9.

5.2 Micropump chemical compatibility

DOI: http://dx.doi.org/10.5772/intechopen.82857

Medium (/) Dynamic viscosity

(mPas)

Typical micropump performance evaluation for different media.

Time stability for two types of PZT, driven at limiting amplitudes.

Figure 8 shows how flow rate increases linearly with excitation amplitude and is stable with time. This is true at each point shown until the amplitude level of 110 V for the presented case. However, when abovementioned amplitude was exceeded (which might be below the value specified by manufacturers), the flow does not respond in a linear manner and also the time stability of flow rate (as being checked at each point shown) is not maintained. After reverting to lower voltages again, the flow is irreversibly reduced, showing that PZT actuator is severely affected when

Figure 8. Excitation amplitude safe operation range and reduced flow when exceeding the limiting amplitude.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

Figure 9. Time stability for two types of PZT, driven at limiting amplitudes.

overdriven. Instead, it behaves as shown in Figure 9, and at 140 V, (shown for two distinct manufacturers) one preserved the air flow stability, the other deteriorated rapidly.

#### 5.2 Micropump chemical compatibility

Constituent materials of the micropump being in direct contact with medium, each having its specific chemical and mechanical properties, should withstand longterm micropump operation without failure. It is therefore mandatory to determine their chemical resistance and fatigue issues. In this respect, a variety of media with distinct pH and different viscosities should also be included in micropump quality control test set. To provide reliable data in the specification list, the micropump tests were performed under continuous operation in the time period between 10 and 300 hours. A set of presented tests, summarized in Table 1, comprised common


#### Table 1.

Typical micropump performance evaluation for different media.

operation area) and is one of quality criteria finally reflected through the pump

Quality Management and Quality Control - New Trends and Developments

Excitation amplitude safe operation range and reduced flow when exceeding the limiting amplitude.

Figure 8 shows how flow rate increases linearly with excitation amplitude and is stable with time. This is true at each point shown until the amplitude level of 110 V for the presented case. However, when abovementioned amplitude was exceeded (which might be below the value specified by manufacturers), the flow does not respond in a linear manner and also the time stability of flow rate (as being checked at each point shown) is not maintained. After reverting to lower voltages again, the flow is irreversibly reduced, showing that PZT actuator is severely affected when

performance deterioration.

PZT d33 modulus stability vs. excitation signal amplitude.

Figure 7.

Figure 8.

104

liquids that might be potentially encountered for pumping in a laboratory or industrial R&D environment.

Micropump materials exposed directly to the chemicals in the presented case are Tygon ND 100-65 tubes, ABS polymer substrate, glass membrane, and PDMS channel. Tests were performed by continuous pumping from a 5 ml reservoir of fluid in a closed loop system.

One criterion to reassure quality and compatibility was to monitor the flow rate variations over period of time. It can vary due to deterioration of materials themselves or due to particles that can cause obstructions in pumping chamber or in throttle region, since the tests were performed without any additional filtering. After the tests were completed, the flow rate of DI water should be maintained as compared to values obtained prior to tests. This will confirm that the constituent materials are chemically resistant to the media tested. Careful optical inspection of potential obstructions was found at throttle only due to unfiltered tap water and none of potential products (aggregates) due to unexpected chemical reaction between the aggressive media and pump materials. It should be kept in mind that for high viscosity medium, such as glycol, the excitation frequency should be lowered to obtain optimal flow rate. Phosphate-buffered solution (PBS) and physiological solution (0.9% NaCl) were also successfully pumped for 6 hours with constant flow rate, showing the pump is useful for biological experiments.

Alcohols and solvents are particular group of media that require careful consideration. PDMS, which is used in presented micropumps, is not compatible with latter as it is subdued to swelling when exposed to solvents. It was determined that

In principle, presented micropumps are intended to pump liquids, however, one of the figures of merit is the pump self-priming parameter, that is, the ability of the dry micropump to pump air until the liquid is dragged into the micropump chamber from the reservoir, which might be in certain cases located below the

After several experimentally performed priming tests, it was determined that one should strictly distinguish between three approaches to define micropump priming property as the values may differ significantly: First approach is to measure air suction pressure (SP) at pump inlet by means of pressure sensor, with the outlet open to atmosphere. The second approach is to suck the liquid from the reservoir located well below the pump level and measure the height of water column in the tube up to which the pump drags the medium and holds it there (named "quasi priming"). It was determined that the latter two values do not necessarily exhibit the same values. Third, the most rigorous approach and the only relevant priming value is accomplished when the pump drags the water column from the reservoir below into the pumping chamber and fluid appears at the pump outlet. The height difference between a water level in a reservoir and the pump in this "real priming" gives always lower values (35–50%) than the previous two priming criteria. The differences and a noteworthy proportionality of the obtained values for a representative run of eight micropump samples are presented in Figure 12(left). Quality control should as well consider users scenarios such as semi dry pump priming (e.g., usage after extended periods in idle state with partially remained water inside). Micropumps have to be repeatedly tested to reveal the safety margins and to set the user specs, so the pump survives a potential misuse. In addition, selfpriming is a function of actuator driving parameters, such as voltage, signal waveform, and frequency as shown in Figure 12(right). Here, the priming response is linear with increasing frequency for voltages below or equal 110 V, while above this

swelling reduces the geometry of gaps and obstructs the flow irreversibly.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

DOI: http://dx.doi.org/10.5772/intechopen.82857

Continuous long-term pump operation for three aggressive media and DI water.

5.3 Self-priming

Figure 11.

micropump level.

107

Furthermore, micropump was subdued to even more rigorous tests with a set of aggressive media to evaluate chemical resistance. One of the potential proposed applications of micropump was to periodically replenish small amounts of solutions in electroplating tin and nickel baths. Exact compositions of solutions given by industrial partner were not revealed, but are commonly used in metal electroplating industry. First, we determined pH and specific gravity of each to convert it into flow rate. It should be mentioned that during these tests, the same pump was used for all three liquids. DI water purging between each medium test was performed and exactly measuring a reference DI flow rate prior to, between the tests and after tests. Short term stability was first monitored for 2 hours for each media (Figure 10), followed by separate long-term tests (Figure 11). The properties of aggressive media, flow rate, and test duration are given in Table 1. The raw data can be further used to set the flow control loop.

Figure 10. Continuous short-term pump operation for three aggressive media and DI water.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

#### Figure 11. Continuous long-term pump operation for three aggressive media and DI water.

Alcohols and solvents are particular group of media that require careful consideration. PDMS, which is used in presented micropumps, is not compatible with latter as it is subdued to swelling when exposed to solvents. It was determined that swelling reduces the geometry of gaps and obstructs the flow irreversibly.

#### 5.3 Self-priming

liquids that might be potentially encountered for pumping in a laboratory or indus-

Tygon ND 100-65 tubes, ABS polymer substrate, glass membrane, and PDMS channel. Tests were performed by continuous pumping from a 5 ml reservoir of

Quality Management and Quality Control - New Trends and Developments

Micropump materials exposed directly to the chemicals in the presented case are

One criterion to reassure quality and compatibility was to monitor the flow rate variations over period of time. It can vary due to deterioration of materials themselves or due to particles that can cause obstructions in pumping chamber or in throttle region, since the tests were performed without any additional filtering. After the tests were completed, the flow rate of DI water should be maintained as compared to values obtained prior to tests. This will confirm that the constituent materials are chemically resistant to the media tested. Careful optical inspection of potential obstructions was found at throttle only due to unfiltered tap water and none of potential products (aggregates) due to unexpected chemical reaction between the aggressive media and pump materials. It should be kept in mind that for high viscosity medium, such as glycol, the excitation frequency should be lowered to obtain optimal flow rate. Phosphate-buffered solution (PBS) and physiological solution (0.9% NaCl) were also successfully pumped for 6 hours with constant flow rate, showing the pump is useful for biological experiments.

Furthermore, micropump was subdued to even more rigorous tests with a set of aggressive media to evaluate chemical resistance. One of the potential proposed applications of micropump was to periodically replenish small amounts of solutions in electroplating tin and nickel baths. Exact compositions of solutions given by industrial partner were not revealed, but are commonly used in metal electroplating industry. First, we determined pH and specific gravity of each to convert it into flow rate. It should be mentioned that during these tests, the same pump was used for all three liquids. DI water purging between each medium test was performed and exactly measuring a reference DI flow rate prior to, between the tests and after

tests. Short term stability was first monitored for 2 hours for each media

Continuous short-term pump operation for three aggressive media and DI water.

be further used to set the flow control loop.

Figure 10.

106

(Figure 10), followed by separate long-term tests (Figure 11). The properties of aggressive media, flow rate, and test duration are given in Table 1. The raw data can

trial R&D environment.

fluid in a closed loop system.

In principle, presented micropumps are intended to pump liquids, however, one of the figures of merit is the pump self-priming parameter, that is, the ability of the dry micropump to pump air until the liquid is dragged into the micropump chamber from the reservoir, which might be in certain cases located below the micropump level.

After several experimentally performed priming tests, it was determined that one should strictly distinguish between three approaches to define micropump priming property as the values may differ significantly: First approach is to measure air suction pressure (SP) at pump inlet by means of pressure sensor, with the outlet open to atmosphere. The second approach is to suck the liquid from the reservoir located well below the pump level and measure the height of water column in the tube up to which the pump drags the medium and holds it there (named "quasi priming"). It was determined that the latter two values do not necessarily exhibit the same values. Third, the most rigorous approach and the only relevant priming value is accomplished when the pump drags the water column from the reservoir below into the pumping chamber and fluid appears at the pump outlet. The height difference between a water level in a reservoir and the pump in this "real priming" gives always lower values (35–50%) than the previous two priming criteria. The differences and a noteworthy proportionality of the obtained values for a representative run of eight micropump samples are presented in Figure 12(left). Quality control should as well consider users scenarios such as semi dry pump priming (e.g., usage after extended periods in idle state with partially remained water inside). Micropumps have to be repeatedly tested to reveal the safety margins and to set the user specs, so the pump survives a potential misuse. In addition, selfpriming is a function of actuator driving parameters, such as voltage, signal waveform, and frequency as shown in Figure 12(right). Here, the priming response is linear with increasing frequency for voltages below or equal 110 V, while above this

Figure 12.

Micropump priming comparison, based on self-priming methods (left). Self-priming vs. actuator driving voltage, signal waveform and frequency (right).

value tends to be influenced by PZT degradation and/or self-heating as shown previously in Figures 8 and 9.

> respect, it is further very important to take into account as well the strong temperature dependency of the medium viscosity, which is additionally affecting the flowpressure performance. For example, water dynamic viscosity is known from the literature to decrease by ca. 30% in the temperature range between 20 and 35°C, while the water density decreases only by 0.4% in the same temperature range and is therefore negligible if we want to introduce correction method. It was experimentally determined that for deionized water, the increase of flow rate with temperature closely follows the well-known decrease of viscosity but only up to 42°C (Figure 14). As shown, flow rate above this temperature tends to decrease rapidly. It is assumed that above this point, the temperature dependency of material properties, such as PDMS and PZT actuator tend to deteriorate the pump performances.

Bubble tolerance correlation with other micropump performance parameters for run of five micropumps.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

DOI: http://dx.doi.org/10.5772/intechopen.82857

Besides, at higher temperature, additional microfluidic phenomena such as degassing and cavitation might contribute to flow rate decrease. Based on these experimental data, we included the above temperature-dependent viscosity

Figure 14.

109

Figure 13.

Pump flow rate vs. DI water temperature.

#### 5.4 Bubble tolerance

In particular cases, when the media flow in the pump supply line is disrupted by sporadic gas bubbles, formed from various reasons [14], the pump has to be able to continuously operate with both media; not only at open outlet (without load) but as well at defined load (backpressure-BP), which should be considered a common situation in real application. This is so called bubble tolerance (BT) parameter and is an additional micropump figure of merit. It is mainly a function of cylinder, throttle, and chamber design and geometry. By narrowing the gaps between membrane and cylinder/throttle and by decreasing micropump chamber depth, rectifying elements efficiency and compression ratio, respectively, are improved [15]. A combination of high rectifying elements efficiency yielding good backpressure for pumping liquid (load dependent) and high compression ratio yielding ability to pump air (expelling air from the cylinder) lead to bubble tolerant micropump. There are approaches to avoid such air bubble disruptions but require additional devices or degassing methods, which is inconvenient [14]. In our methodology, bubble tolerance test is performed by interrupting a continuous DI water flow with the introduction of air slugs, 2–4 mm long into the pump suction inlet tube (ID = 1.5 mm) every 10 seconds. This was performed as long as the water column at the outlet tube built up. Final height of output water column is proportional to the maximal backpressure at which the pump still digests air bubbles and continuous DI water pumping is ceased. The operating safe area should be set below this point, according to its known flow rate vs. backpressure characteristics. As determined empirically, qualitative criterion can be obtained as well from other measured parameters. By comparing seven measured micropump parameters for each of five pumps from the same run (Figure 13), it was determined that there is the strongest correlation of bubble tolerance with air flow and water backpressure performances as discussed above. In quality control process, this enables us to evaluate the property without performing explicit, time-consuming BT testing for each micropump.

#### 5.5 Temperature dependency of flow rate

It is well-known that micropump flow rate is inversely proportional to medium viscosity as given by Poiseuille expression for flow inside the microchannel. In this Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

Figure 13. Bubble tolerance correlation with other micropump performance parameters for run of five micropumps.

respect, it is further very important to take into account as well the strong temperature dependency of the medium viscosity, which is additionally affecting the flowpressure performance. For example, water dynamic viscosity is known from the literature to decrease by ca. 30% in the temperature range between 20 and 35°C, while the water density decreases only by 0.4% in the same temperature range and is therefore negligible if we want to introduce correction method. It was experimentally determined that for deionized water, the increase of flow rate with temperature closely follows the well-known decrease of viscosity but only up to 42°C (Figure 14). As shown, flow rate above this temperature tends to decrease rapidly. It is assumed that above this point, the temperature dependency of material properties, such as PDMS and PZT actuator tend to deteriorate the pump performances. Besides, at higher temperature, additional microfluidic phenomena such as degassing and cavitation might contribute to flow rate decrease. Based on these experimental data, we included the above temperature-dependent viscosity

Figure 14. Pump flow rate vs. DI water temperature.

value tends to be influenced by PZT degradation and/or self-heating as shown

Micropump priming comparison, based on self-priming methods (left). Self-priming vs. actuator driving

Quality Management and Quality Control - New Trends and Developments

the introduction of air slugs, 2–4 mm long into the pump suction inlet tube

5.5 Temperature dependency of flow rate

108

(ID = 1.5 mm) every 10 seconds. This was performed as long as the water column at the outlet tube built up. Final height of output water column is proportional to the maximal backpressure at which the pump still digests air bubbles and continuous DI water pumping is ceased. The operating safe area should be set below this point, according to its known flow rate vs. backpressure characteristics. As determined empirically, qualitative criterion can be obtained as well from other measured parameters. By comparing seven measured micropump parameters for each of five pumps from the same run (Figure 13), it was determined that there is the strongest correlation of bubble tolerance with air flow and water backpressure performances as discussed above. In quality control process, this enables us to evaluate the property without performing explicit, time-consuming BT testing for each micropump.

It is well-known that micropump flow rate is inversely proportional to medium viscosity as given by Poiseuille expression for flow inside the microchannel. In this

In particular cases, when the media flow in the pump supply line is disrupted by sporadic gas bubbles, formed from various reasons [14], the pump has to be able to continuously operate with both media; not only at open outlet (without load) but as well at defined load (backpressure-BP), which should be considered a common situation in real application. This is so called bubble tolerance (BT) parameter and is an additional micropump figure of merit. It is mainly a function of cylinder, throttle, and chamber design and geometry. By narrowing the gaps between membrane and cylinder/throttle and by decreasing micropump chamber depth, rectifying elements efficiency and compression ratio, respectively, are improved [15]. A combination of high rectifying elements efficiency yielding good backpressure for pumping liquid (load dependent) and high compression ratio yielding ability to pump air (expelling air from the cylinder) lead to bubble tolerant micropump. There are approaches to avoid such air bubble disruptions but require additional devices or degassing methods, which is inconvenient [14]. In our methodology, bubble tolerance test is performed by interrupting a continuous DI water flow with

previously in Figures 8 and 9.

voltage, signal waveform and frequency (right).

5.4 Bubble tolerance

Figure 12.

correction factor in the results of our long-term flow rate stability tests as shown in Figure 15. Two micropumps were continuously pumping DI water in closed loop for a period of 27 weeks without particular ambient temperature control. The temperature and flow rate variations were measured periodically. It is very evident that flow rate variations (lines without symbols) are closely related to temperature variations (Figure 14, full circles). By implementing the correction for a temperature dependency of viscosity obtained from Figure 15, the apparent flow rate variations were mitigated, meaning that pump performed more stable that shown by raw data. In general, taking into account the correction around reference temperature, 20°C, which accounted for 0.9%/°C the flow rate variations for pump A is realistically improved from a 26% decrease over 27 weeks to 12% and similarly for pump B (Figure 15, hollow symbols).

#### 5.6 Heat dissipation

In most applications, PZT actuators are driven at high electric field magnitudes and/or high frequencies. Beside the useful conversion into mechanical work, a significant amount of heat is generated within nonideal PZT. Heat generation can considerably affect the reliability and piezoelectric properties of micropump actuators, and may also limit their application since it heats the adjacent materials, and at last but not least also the pumping medium. Self-heating, that is, heat generation within the piezoelectric actuator due to electrical and mechanical losses, is a major concern for high-frequency applications, where increased stress and even degradation of the actuator is expected. In sinusoidal excitation, the average power dissipation P in a piezoelectric actuator can be estimated using the expression below,

$$I^\nu - \frac{\pi}{\cdot \!\!\! } f \Gamma \, \tan \partial \mathcal{E}\_{\,\!\!\!\!\!\!\!/} \, \tag{1}$$

evaluation of natural or forced convection. It has to be noted as well that piezo ceramics has low heat conductivity but rather high heat capacity, which affects the thermal time constants. It can be found in the literature that for a standard PZT actuator under small-signal conditions, up to 2% of the electrical energy flowing through the actuator is converted into heat. In large-signal conditions, however, 8–12% of the electrical energy pumped into the actuator is converted to heat. Therefore, increased operating temperature can strongly affect the piezo actuator

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric…

DOI: http://dx.doi.org/10.5772/intechopen.82857

Interrelation of temperature due to PZT heat dissipation and micropump air flow rate.

Our recommended approach to determine and characterize how a particular micropump system behaves thermally is to monitor temperature of PZT and/or pumping medium directly by using a temperature sensor mounted on/near the PZT and perform measurements during the micropump operation. This should be correlated with measurements of flow rate or other performance variations. A miniature Pt-100 temperature sensor in our case was mounted atop the PZT disc with special emphasis not to disturb the operation and minimize damping. Once knowing the temperature conditions of PZT, temperature sensor can be placed next to

A very illustrative example of interrelation between PZT temperature and air flow rate is given in Figure 16 for micropump driven at normal actuating regime. The proposed type of measurements is very useful particularly in pumping systems, where high-flow rate accuracy is required. The measured temperature dependency of flow rate can be further included in compensation algorithm of control loop.

For a case study of piezoelectric micropumps quality control, an innovative microcylinder pump developed in our laboratory was selected. Quality control is given by extensive evaluation methodology for assessing mechanical properties of constituent micropump components (Young's modulus of PDMS elastomer and d31 modulus of PZT actuator), reliability, and stability of micropump operation (selfpriming, bubble tolerance, pumping media chemical compatibility, and heat dissipation) and quality of fabrication process (covalent bond strength, bond hydrolytic stability, and plastic housing surface flatness). Namely, irregular flatness of ABS

PZT on glass membrane for continuous monitoring purposes.

dynamics.

Figure 16.

6. Conclusion

111

where tan δ is the dielectric dissipation factor, C is apparent PZT actuator capacitance, Upp is peak-to-peak operating voltage, and f is the operating frequency.

To be able to evaluate the thermal response of the micropump as a thermal system, it is necessary to know the geometry and thermal properties of individual materials such as thermal conduction, free surfaces, fluid type, and flow for the

Figure 15. Long-term testing and flow rate correction due to temperature dependent viscosity of water.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

#### Figure 16.

correction factor in the results of our long-term flow rate stability tests as shown in Figure 15. Two micropumps were continuously pumping DI water in closed loop for a period of 27 weeks without particular ambient temperature control. The temperature and flow rate variations were measured periodically. It is very evident that flow rate variations (lines without symbols) are closely related to temperature variations (Figure 14, full circles). By implementing the correction for a temperature dependency of viscosity obtained from Figure 15, the apparent flow rate variations were mitigated, meaning that pump performed more stable that shown by raw data. In general, taking into account the correction around reference temperature, 20°C, which accounted for 0.9%/°C the flow rate variations for pump A is realistically improved from a 26% decrease over 27 weeks to 12% and similarly for

Quality Management and Quality Control - New Trends and Developments

In most applications, PZT actuators are driven at high electric field magnitudes

(1)

and/or high frequencies. Beside the useful conversion into mechanical work, a significant amount of heat is generated within nonideal PZT. Heat generation can considerably affect the reliability and piezoelectric properties of micropump actuators, and may also limit their application since it heats the adjacent materials, and at last but not least also the pumping medium. Self-heating, that is, heat generation within the piezoelectric actuator due to electrical and mechanical losses, is a major concern for high-frequency applications, where increased stress and even degradation of the actuator is expected. In sinusoidal excitation, the average power dissipation P in a piezoelectric actuator can be estimated using the expression below,

where tan δ is the dielectric dissipation factor, C is apparent PZT actuator capacitance, Upp is peak-to-peak operating voltage, and f is the operating frequency. To be able to evaluate the thermal response of the micropump as a thermal system, it is necessary to know the geometry and thermal properties of individual materials such as thermal conduction, free surfaces, fluid type, and flow for the

Long-term testing and flow rate correction due to temperature dependent viscosity of water.

pump B (Figure 15, hollow symbols).

5.6 Heat dissipation

Figure 15.

110

Interrelation of temperature due to PZT heat dissipation and micropump air flow rate.

evaluation of natural or forced convection. It has to be noted as well that piezo ceramics has low heat conductivity but rather high heat capacity, which affects the thermal time constants. It can be found in the literature that for a standard PZT actuator under small-signal conditions, up to 2% of the electrical energy flowing through the actuator is converted into heat. In large-signal conditions, however, 8–12% of the electrical energy pumped into the actuator is converted to heat. Therefore, increased operating temperature can strongly affect the piezo actuator dynamics.

Our recommended approach to determine and characterize how a particular micropump system behaves thermally is to monitor temperature of PZT and/or pumping medium directly by using a temperature sensor mounted on/near the PZT and perform measurements during the micropump operation. This should be correlated with measurements of flow rate or other performance variations. A miniature Pt-100 temperature sensor in our case was mounted atop the PZT disc with special emphasis not to disturb the operation and minimize damping. Once knowing the temperature conditions of PZT, temperature sensor can be placed next to PZT on glass membrane for continuous monitoring purposes.

A very illustrative example of interrelation between PZT temperature and air flow rate is given in Figure 16 for micropump driven at normal actuating regime. The proposed type of measurements is very useful particularly in pumping systems, where high-flow rate accuracy is required. The measured temperature dependency of flow rate can be further included in compensation algorithm of control loop.

#### 6. Conclusion

For a case study of piezoelectric micropumps quality control, an innovative microcylinder pump developed in our laboratory was selected. Quality control is given by extensive evaluation methodology for assessing mechanical properties of constituent micropump components (Young's modulus of PDMS elastomer and d31 modulus of PZT actuator), reliability, and stability of micropump operation (selfpriming, bubble tolerance, pumping media chemical compatibility, and heat dissipation) and quality of fabrication process (covalent bond strength, bond hydrolytic stability, and plastic housing surface flatness). Namely, irregular flatness of ABS

substrate directly transfers on the membrane via PDMS elastomer layer. This results in sticking of rectifying elements thus causing micropump malfunction. It is shown herein that micropump operating stability is closely related to PZT excitation signal amplitude, which might cause deterioration of piezoelectric actuator. Degradation of d31 modulus due to PZT depolarization or fatigue directly effects micropump flowrate and backpressure performance. In this respect, safe operating area needs to be determined. The methodology to determine self-priming ability criteria is given. It is further shown that in quality control of micropump operation, the bubble tolerance can be estimated indirectly through the micropump airflow and water backpressure performance. Finally, it is shown that temperature dependency of flow rate has to be taken into account. It was determined that it reflects mainly through variations in viscosity at lower temperatures and temperature dependency of material properties of PZT and PDMS at elevated temperature.

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#### Acknowledgements

This work was performed within the framework of a project supported by the Slovenian industrial partner KOLEKTOR Group d.o.o., Vojkova 10, 5280 Idrija Slovenia and the Ministry of Education, Science, Culture and Sport (Grant No P2-0244).

#### Author details

Matej Možek\*, Borut Pečar, Drago Resnik and Danilo Vrtačnik Laboratory of Microsensor Structures and Electronics (LMSE), Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia

\*Address all correspondence to: matej.mozek@fe.uni-lj.si

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Determination of Essential Parameters for Quality Control in Fabrication of Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.82857

#### References

substrate directly transfers on the membrane via PDMS elastomer layer. This results in sticking of rectifying elements thus causing micropump malfunction. It is shown herein that micropump operating stability is closely related to PZT excitation signal amplitude, which might cause deterioration of piezoelectric actuator. Degradation of d31 modulus due to PZT depolarization or fatigue directly effects micropump flowrate and backpressure performance. In this respect, safe operating area needs to be determined. The methodology to determine self-priming ability criteria is given. It is further shown that in quality control of micropump operation, the bubble tolerance can be estimated indirectly through the micropump airflow and water backpressure performance. Finally, it is shown that temperature dependency of flow rate has to be taken into account. It was determined that it reflects mainly through variations in viscosity at lower temperatures and temperature dependency

This work was performed within the framework of a project supported by the Slovenian industrial partner KOLEKTOR Group d.o.o., Vojkova 10, 5280 Idrija Slovenia and the Ministry of Education, Science, Culture and Sport (Grant No

of material properties of PZT and PDMS at elevated temperature.

Quality Management and Quality Control - New Trends and Developments

Matej Možek\*, Borut Pečar, Drago Resnik and Danilo Vrtačnik

Engineering, University of Ljubljana, Ljubljana, Slovenia

\*Address all correspondence to: matej.mozek@fe.uni-lj.si

provided the original work is properly cited.

Laboratory of Microsensor Structures and Electronics (LMSE), Faculty of Electrical

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Acknowledgements

P2-0244).

Author details

112

[1] Kamei KI, Kato Y, Hirai Y, Ito S, Satoh J, Oka A, et al. Integrated heart/ cancer on a chip to reproduce the side effects of anti-cancer drugs in vitro. RSC Advances. 2017;7(58):36777-36786

[2] Minteer S. Alcoholic Fuels. CRC Press; 2016

[3] Liu Y, Li G. A power-free, parallel loading microfluidic reactor array for biochemical screening. Scientific Reports, Nature. 2018;8(1):13664

[4] Vijaya MS. Piezoelectric Materials and Devices: Applications in Engineering and Medical Sciences. CRC Press; 2016

[5] Dolžan T, Pečar B, Možek M, Resnik D, Vrtačnik D. Self-priming bubble tolerant microcylinder pump. Sensors and Actuators A: Physical. 2015;233: 548-556

[6] Suzuki Y, Yamada M, Seki M. Sol-gel based fabrication of hybrid microfluidic devices composed of PDMS and thermoplastic substrates. Sensors and Actuators B: Chemical. 2010;148(1): 323-329

[7] Tsao CW, DeVoe DL. Bonding of thermoplastic polymer microfluidics. Microfluidics and Nanofluidics. 2009; 6(1):1-16

[8] Wu J, Lee NY. One-step surface modification for irreversible bonding of various plastics with a poly (dimethylsiloxane) elastomer at room temperature. Lab on a Chip. 2014;14(9): 1564-1571

[9] Pečar B, Možek M, Vrtačnik D. Thermoplastic-PDMS polymer covalent bonding for microfluidic applications. Informacije MIDEM. 2017;47(3): 147-154

[10] Lee SK, Lee H, Ram JR. U.S. Patent No. 9,422,409. Washington, DC: U.S. Patent and Trademark Office; 2016

[11] Lee KS, Ram RJ. Plastic–PDMS bonding for high pressure hydrolytically stable active microfluidics. Lab on a Chip. 2009;9(11):1618-1624

[12] Johnston ID, McCluskey DK, Tan CKL, Tracey MC. Mechanical characterization of bulk Sylgard 184 for microfluidics and microengineering. Journal of Micromechanics and Microengineering. 2014;24(3):035017

[13] Genenko YA, Glaum J, Hoffmann MJ, Albe K. Mechanisms of aging and fatigue in ferroelectrics. Materials Science and Engineering: B. 2015;192: 52-82

[14] Jenke C, Kager S, Richter M, Kutter C. Flow rate influencing effects of micropumps. Sensors and Actuators A: Physical. 2018;276:335-345

[15] Richter M, Linnemann R, Woias P. Robust design of gas and liquid micropumps. Sensors and Actuators. 1998

**115**

**Chapter 7**

**Abstract**

identification results.

**1. Introduction**

ingredient" [1].

stable isotope distribution patterns

Determination of Impurities in

*Kung-Tien Liu and Chien-Hsin Chen*

Pharmaceuticals: Why and How?

The presence of impurities, particularly the API-related impurities, i.e., degradation-related impurities (DRIs) and interaction-related impurities (IRIs), may affect the quality, safety, and efficacy of drug products. Since the regulatory requirements and management strategies are required to be established and complied, sources of impurities shall be carefully classified prior to take subsequent steps such as development of analytical methods and acceptance criteria. Current international regulatory requirements for the management of impurities in pharmaceuticals were reviewed. Procedures for the identification of DPIs in pharmaceuticals, i.e., ethyl cysteinate dimer, (R)-N-methyl-3-(2-bromophenoxy) -3-phenylpropanamine, sestamibi, etc., using high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS) were studied. Scheme for the establishment of analytical methods and acceptance criteria of process-related impurities (PRIs) and DRIs in accordance with the requirements of International Council for Harmonization (ICH) and algorithm to perform the identification of DPIs by using LC-MS/MS has been proposed. Practice of kinetic study to distinguish PRIs and DRIs, determination of the potential core fragments coupled with a predicted list of relevant transformations for conducting MS/MS scans, applications of stable isotope distribution patterns or natural abundances, practice of mass balance, etc., have been well demonstrated to justify the reliabilities of

**Keywords:** pharmaceutical products, impurities, regulatory requirements, analytical strategy, structural identification, validation, verification, LC-MS/MS, kinetic study,

As defined by the United States Pharmacopeial (USP), impurity is "any component of a drug substance that is not the chemical entity defined as the drug substance and in addition, for a drug product, any component that is not a formulation

Impurities in drug substance (i.e., active pharmaceutical ingredient, API) or drug product can arise due to synthetic/manufacturing processes, degradation, storage conditions, container, excipients, or contamination. They can be identified

Since different regulatory requirements and management strategies are required to be established and complied, sources of impurities shall be carefully classified

or unidentified, volatile or nonvolatile, organic or inorganic species [1–3].

#### **Chapter 7**

## Determination of Impurities in Pharmaceuticals: Why and How?

*Kung-Tien Liu and Chien-Hsin Chen*

#### **Abstract**

The presence of impurities, particularly the API-related impurities, i.e., degradation-related impurities (DRIs) and interaction-related impurities (IRIs), may affect the quality, safety, and efficacy of drug products. Since the regulatory requirements and management strategies are required to be established and complied, sources of impurities shall be carefully classified prior to take subsequent steps such as development of analytical methods and acceptance criteria. Current international regulatory requirements for the management of impurities in pharmaceuticals were reviewed. Procedures for the identification of DPIs in pharmaceuticals, i.e., ethyl cysteinate dimer, (R)-N-methyl-3-(2-bromophenoxy) -3-phenylpropanamine, sestamibi, etc., using high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS) were studied. Scheme for the establishment of analytical methods and acceptance criteria of process-related impurities (PRIs) and DRIs in accordance with the requirements of International Council for Harmonization (ICH) and algorithm to perform the identification of DPIs by using LC-MS/MS has been proposed. Practice of kinetic study to distinguish PRIs and DRIs, determination of the potential core fragments coupled with a predicted list of relevant transformations for conducting MS/MS scans, applications of stable isotope distribution patterns or natural abundances, practice of mass balance, etc., have been well demonstrated to justify the reliabilities of identification results.

**Keywords:** pharmaceutical products, impurities, regulatory requirements, analytical strategy, structural identification, validation, verification, LC-MS/MS, kinetic study, stable isotope distribution patterns

#### **1. Introduction**

As defined by the United States Pharmacopeial (USP), impurity is "any component of a drug substance that is not the chemical entity defined as the drug substance and in addition, for a drug product, any component that is not a formulation ingredient" [1].

Impurities in drug substance (i.e., active pharmaceutical ingredient, API) or drug product can arise due to synthetic/manufacturing processes, degradation, storage conditions, container, excipients, or contamination. They can be identified or unidentified, volatile or nonvolatile, organic or inorganic species [1–3].

Since different regulatory requirements and management strategies are required to be established and complied, sources of impurities shall be carefully classified

#### *Quality Management and Quality Control - New Trends and Developments*

prior to take subsequent steps; for instance, to distinguish an impurity which is simply derived from API alone or actually derived from interaction products of APIexcipient, excipient-excipient, or API-residual impurities existing in excipients [4–6].

Despite an increase in the research of impurities, a number of problems are still arisen in the development of identification technologies for degradation products and pathways. The first aim of this research is to address a brief review of the current major international regulatory requirements regarding the management of impurities in pharmaceutical products. Then secondly, a general scheme to establish an analytical method and acceptance criteria of degradation-related impurities (DRIs) and process-related impurities (PRIs) can be proposed, accordingly. Finally, our research will focus on developing a practicable algorithm to perform the identification of DPIs by using high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). Meanwhile, verification method for the justification of reliabilities regarding identification results will be assessed.

#### **1.1 Classification of impurities**

According to the definitions of International Council for Harmonization (ICH), Food and Drug Administration (FDA), and USP, impurities are classified into DRIs, PRIs, residual solvents, and heavy metals as shown in **Figure 1** [1, 2, 7].

Two types of impurities might be API-related. The first type of API-related impurities is generated by degradation of API itself under specific storage conditions, e.g., oxidation, dehydration, carbon dioxide removal, etc. The other type is occurred due to the interaction between API and excipients, container, or residual impurities in excipients, reagents, or solvents [8, 9]. API-related impurities are potentially genotoxic, mutagenic, and carcinogenic risk due to their structureactivity relationship (SRA) [10, 11].

**117**

**Table 1.**

*Determination of Impurities in Pharmaceuticals: Why and How?*

uncertain risks to the stability or quality of products [15].

requirements and scientific/technical demands (**Table 1**).

APIs and drug products [1, 16, 17].

**1.2 Aims to conduct impurity study**

• Quality and safety of products • Method validation, i.e., specificity • Acceptance criteria determination

exposure (PDE), etc.

• Expiry date, retest date, and shelf-life evaluation

*Examples of the aims to conduct impurity studies [20, 23, 25–27].*

• Stability and storage conditions study • Threshold limits evaluation, i.e., threshold of toxicological concern (TTC), permitted daily

It is well known that excipients or the residual impurities in excipients can be very likely to cause instability of the API and drug product. A lot of impurities in excipients, such as presence of reactive peroxides or high water content in povidone or polyethylene glycols (PEGs), antioxidants in magnesium stearate, aldehydes in lactose, benzaldehyde in benzyl alcohol, formaldehyde in starch, lignin and hemicelluloses in microcrystalline cellulose were illustrated to demonstrate how reactive chemical entities are commonplace in excipients and incompatible to API. Some specific functional groups in API may be susceptible to degradation mechanisms, i.e., hydrolysis, oxidation, polymerization, etc.

Additionally, extractables and leachables such as initiators/catalysts, storage stabilizers, antioxidants, processing aids, light stabilizers, antistatic agents, colorants, lubricants associated with pharmaceutically relevant materials may also produce

Study of impurities in pharmaceuticals is one of the most highly regarded topics;

it is essential, but time consuming and challenging. In terms of regulations and technology, we must keep pace with the times [18, 19]. Comprehensively speaking, aims to develop an impurity study have two major directions as follows: regulatory

From the perspective of regulatory requirements, impurities may affect the quality of APIs and DPs and ultimately affect the safety of the patient. Views for the dealing of impurities may differ between biologists, toxicologists, and analytical chemists, and therefore need to be integrated [20]. Potential genotoxic impurities can be determined according to the published literature, results of gene mutation in bacteria, in vitro and in vivo tests of chromosomal damage in mammalian cells or rodent hematopoietic cells, or/and comparative structural analysis to identify chemical functional moieties correlated with mutagenicity [16]. Moreover, daily exposure, duration of exposure on the effects of degradation products and genotoxic impurities, and theoretical clinical dose, whereas potential

**Regulatory requirements Scientific and technical requirements**

• Synthetic and production processes

• Manufacturing of reference materials

• Formulation development and optimization

optimization

• Efficacy improvement • ADME and toxicology study

• Stability improvement • DPIs and pathways prediction

• Cost consideration

Regardless of the classes of impurities, presence of impurities may have the potential to affect the quality, safety, and efficacy of drug products. Therefore, studies of impurities are one of the most important works in the development of

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

[4–6, 12–14].

#### **Figure 1.** *Classification of impurities [1, 2, 7].*

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

*Quality Management and Quality Control - New Trends and Developments*

reliabilities regarding identification results will be assessed.

**1.1 Classification of impurities**

activity relationship (SRA) [10, 11].

prior to take subsequent steps; for instance, to distinguish an impurity which is simply derived from API alone or actually derived from interaction products of APIexcipient, excipient-excipient, or API-residual impurities existing in excipients [4–6]. Despite an increase in the research of impurities, a number of problems are still arisen in the development of identification technologies for degradation products and pathways. The first aim of this research is to address a brief review of the current major international regulatory requirements regarding the management of impurities in pharmaceutical products. Then secondly, a general scheme to establish an analytical method and acceptance criteria of degradation-related impurities (DRIs) and process-related impurities (PRIs) can be proposed, accordingly. Finally, our research will focus on developing a practicable algorithm to perform the identification of DPIs by using high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). Meanwhile, verification method for the justification of

According to the definitions of International Council for Harmonization (ICH), Food and Drug Administration (FDA), and USP, impurities are classified into DRIs,

Two types of impurities might be API-related. The first type of API-related impurities is generated by degradation of API itself under specific storage conditions, e.g., oxidation, dehydration, carbon dioxide removal, etc. The other type is occurred due to the interaction between API and excipients, container, or residual impurities in excipients, reagents, or solvents [8, 9]. API-related impurities are potentially genotoxic, mutagenic, and carcinogenic risk due to their structure-

PRIs, residual solvents, and heavy metals as shown in **Figure 1** [1, 2, 7].

**116**

**Figure 1.**

*Classification of impurities [1, 2, 7].*

It is well known that excipients or the residual impurities in excipients can be very likely to cause instability of the API and drug product. A lot of impurities in excipients, such as presence of reactive peroxides or high water content in povidone or polyethylene glycols (PEGs), antioxidants in magnesium stearate, aldehydes in lactose, benzaldehyde in benzyl alcohol, formaldehyde in starch, lignin and hemicelluloses in microcrystalline cellulose were illustrated to demonstrate how reactive chemical entities are commonplace in excipients and incompatible to API. Some specific functional groups in API may be susceptible to degradation mechanisms, i.e., hydrolysis, oxidation, polymerization, etc. [4–6, 12–14].

Additionally, extractables and leachables such as initiators/catalysts, storage stabilizers, antioxidants, processing aids, light stabilizers, antistatic agents, colorants, lubricants associated with pharmaceutically relevant materials may also produce uncertain risks to the stability or quality of products [15].

Regardless of the classes of impurities, presence of impurities may have the potential to affect the quality, safety, and efficacy of drug products. Therefore, studies of impurities are one of the most important works in the development of APIs and drug products [1, 16, 17].

#### **1.2 Aims to conduct impurity study**

Study of impurities in pharmaceuticals is one of the most highly regarded topics; it is essential, but time consuming and challenging. In terms of regulations and technology, we must keep pace with the times [18, 19]. Comprehensively speaking, aims to develop an impurity study have two major directions as follows: regulatory requirements and scientific/technical demands (**Table 1**).

From the perspective of regulatory requirements, impurities may affect the quality of APIs and DPs and ultimately affect the safety of the patient. Views for the dealing of impurities may differ between biologists, toxicologists, and analytical chemists, and therefore need to be integrated [20]. Potential genotoxic impurities can be determined according to the published literature, results of gene mutation in bacteria, in vitro and in vivo tests of chromosomal damage in mammalian cells or rodent hematopoietic cells, or/and comparative structural analysis to identify chemical functional moieties correlated with mutagenicity [16]. Moreover, daily exposure, duration of exposure on the effects of degradation products and genotoxic impurities, and theoretical clinical dose, whereas potential


#### **Table 1.**

*Examples of the aims to conduct impurity studies [20, 23, 25–27].*

mutagenic impurities must be controlled to levels less than the threshold of toxicological concern based on lifetime exposure shall be evaluated as a risk consideration [16–18].

Adequate qualification must include genotoxicity and repeat-dose toxicology studies of appropriate duration to support the proposed indication. Moreover, other specific toxicity studies, e.g., embryofetal developmental toxicity study may be appropriate. Genotoxic impurities and degradation products pose an additional risk and should be controlled in accordance with the requirements of ICH M7(R1), unless they are qualified for safety [18, 21].

In addition to the regulatory requirements, internal and external scientific and technical needs are the second perspective to conduct an impurity study. Impurity determination and forced degradation studies are two of the basic requirements as a tool to predict potential DPIs, to develop analytical method, synthetic processes, and formulation, to receive a better understanding of storage conditions, stability of drug product, and to obtain information of degradation products/pathways, as well as to evaluate the specificity (selectivity) of assay method [22–25].

#### **2. Regulatory requirements for the management of impurity**

A number of international/local guidelines and guidances for the evaluation and control of impurities in drug substances and drug products have been published [1–3, 7–9, 21, 28–38]. Comparison of the application scopes in line with the impurity categories was drawn as indicated in **Figure 2**.

As said by the requirements of ICH Q3A(R2), all types of impurities present in API at a level greater than (>) the identification threshold must conduct studies to characterize their structures, no matter they are shown in any batch manufactured by the proposed commercial process or any degradation product observed in stability studies under recommended storage conditions. Specified identified impurities shall be included in the list of impurities along with specified unidentified impurities that are estimated to be present at a level greater than the identification threshold [2, 7, 33].

Briefly, five major steps for the management of degradation products, no matter they are degradation products of API or reaction products of API with excipient(s) or container closure system, have been requested by the ICH Q3B (R2) and summarized as follows [3]:


#### **Figure 2.**

*Comparison of the application scopes of regulatory guidelines/guidance for the management of impurities in pharmaceutical products [7, 28–34]. \*Not clearly stated in the regulation.*

**119**

less than 10<sup>−</sup><sup>6</sup>

follows [8, 37]:

humans.

3.Class 3: low-toxic solvents.

concerns [21, 32].

*Determination of Impurities in Pharmaceuticals: Why and How?*

1.Confirm which impurities are degradation products?

2.Monitor and/or specify the amount of all degradation products.

3.Summarize all degradation products during manufacture and stability studies.

4.Elucidate and justify a rational evaluation of possible degradation pathway in the drug product or interaction with excipients or container closure system.

5.Establish specifications of all degradation products, including specified identified, specified unidentified, unspecified degradation product with an acceptance criterion of not more than (≤) identification threshold described in Q3B

Specificity (selectivity) of the method applied to determine specified and unspecified degradation product shall be validated. This includes subjecting of API or drug products to stress studies of light, heat, humidity, acid and base hydrolysis, and oxidation to evaluate the HPLC separation resolution, mass balance, etc. [3, 22, 24, 25].

Although Q3B (R2) was developed by ICH to provide guidance on impurities in drug products for new drug applications (NDAs), it is also considered to be applicable to the drug products of abbreviated new drug application (ANDAs) [33].

Regulation requirements regarding genotoxic, mutagenic, and carcinogenic impurities have been published and revised by European Medicine Agency (EMA), FDA, and ICH in 2006, 2008, and 2017, respectively, to describe how to perform assessments and controls, including prevention and reduction of impurities [21, 28, 32]. Concept of threshold of toxicological concern (TTC) has been developed to define an acceptable intake for any unstudied chemical that poses a negligible risk of carcinogenicity or other toxic effects [21]. In general, exposure level of 1.5 μg per person per day (i.e., TTC) for each impurity can be considered as a common acceptable qualification threshold for supporting marketing application. Any impurity found at a level below this threshold generally does not need further safety qualification for genotoxicity and carcinogenicity concerns. The threshold is an estimate of daily exposure expected to result in an upper-bound lifetime risk of cancer of

(one in a million), a risk level that is thought to pose negligible safety

Currently, ICH Q3C is the major guideline related to the management of residual solvents in API, excipients, and drug products (**Figure 2**). In general, solvents that are used in the manufacturing procedures are the required parts to determine [8]. Types of solvents are sorted according to their carcinogenic and genotoxic risks as

1.Class 1: solvents obviously confirmed or strongly suspected to cause cancer in

Elemental impurities may arise from residual catalysts that were added intentionally in synthesis, or may be present as impurities, e.g., through interactions with processing equipment or container/closure systems or by being present in components of the drug product. Because elemental impurities pose toxicological concerns

and do not provide any therapeutic benefit to the patient, their levels in drug

2.Class 2: nongenotoxic and possible carcinogenic risks in animals.

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

(R2), and their total amount.

*Quality Management and Quality Control - New Trends and Developments*

M7(R1), unless they are qualified for safety [18, 21].

specificity (selectivity) of assay method [22–25].

categories was drawn as indicated in **Figure 2**.

threshold [2, 7, 33].

marized as follows [3]:

ation [16–18].

mutagenic impurities must be controlled to levels less than the threshold of toxicological concern based on lifetime exposure shall be evaluated as a risk consider-

Adequate qualification must include genotoxicity and repeat-dose toxicology studies of appropriate duration to support the proposed indication. Moreover, other specific toxicity studies, e.g., embryofetal developmental toxicity study may be appropriate. Genotoxic impurities and degradation products pose an additional risk and should be controlled in accordance with the requirements of ICH

In addition to the regulatory requirements, internal and external scientific and technical needs are the second perspective to conduct an impurity study. Impurity determination and forced degradation studies are two of the basic requirements as a tool to predict potential DPIs, to develop analytical method, synthetic processes, and formulation, to receive a better understanding of storage conditions, stability of drug product, and to obtain information of degradation products/pathways, as well as to evaluate the

A number of international/local guidelines and guidances for the evaluation and control of impurities in drug substances and drug products have been published [1–3, 7–9, 21, 28–38]. Comparison of the application scopes in line with the impurity

As said by the requirements of ICH Q3A(R2), all types of impurities present in API at a level greater than (>) the identification threshold must conduct studies to characterize their structures, no matter they are shown in any batch manufactured by the proposed commercial process or any degradation product observed in stability studies under recommended storage conditions. Specified identified impurities shall be included in the list of impurities along with specified unidentified impurities that are estimated to be present at a level greater than the identification

Briefly, five major steps for the management of degradation products, no matter they are degradation products of API or reaction products of API with excipient(s) or container closure system, have been requested by the ICH Q3B (R2) and sum-

*Comparison of the application scopes of regulatory guidelines/guidance for the management of impurities in* 

*pharmaceutical products [7, 28–34]. \*Not clearly stated in the regulation.*

**2. Regulatory requirements for the management of impurity**

**118**

**Figure 2.**


Specificity (selectivity) of the method applied to determine specified and unspecified degradation product shall be validated. This includes subjecting of API or drug products to stress studies of light, heat, humidity, acid and base hydrolysis, and oxidation to evaluate the HPLC separation resolution, mass balance, etc. [3, 22, 24, 25].

Although Q3B (R2) was developed by ICH to provide guidance on impurities in drug products for new drug applications (NDAs), it is also considered to be applicable to the drug products of abbreviated new drug application (ANDAs) [33].

Regulation requirements regarding genotoxic, mutagenic, and carcinogenic impurities have been published and revised by European Medicine Agency (EMA), FDA, and ICH in 2006, 2008, and 2017, respectively, to describe how to perform assessments and controls, including prevention and reduction of impurities [21, 28, 32].

Concept of threshold of toxicological concern (TTC) has been developed to define an acceptable intake for any unstudied chemical that poses a negligible risk of carcinogenicity or other toxic effects [21]. In general, exposure level of 1.5 μg per person per day (i.e., TTC) for each impurity can be considered as a common acceptable qualification threshold for supporting marketing application. Any impurity found at a level below this threshold generally does not need further safety qualification for genotoxicity and carcinogenicity concerns. The threshold is an estimate of daily exposure expected to result in an upper-bound lifetime risk of cancer of less than 10<sup>−</sup><sup>6</sup> (one in a million), a risk level that is thought to pose negligible safety concerns [21, 32].

Currently, ICH Q3C is the major guideline related to the management of residual solvents in API, excipients, and drug products (**Figure 2**). In general, solvents that are used in the manufacturing procedures are the required parts to determine [8]. Types of solvents are sorted according to their carcinogenic and genotoxic risks as follows [8, 37]:


Elemental impurities may arise from residual catalysts that were added intentionally in synthesis, or may be present as impurities, e.g., through interactions with processing equipment or container/closure systems or by being present in components of the drug product. Because elemental impurities pose toxicological concerns and do not provide any therapeutic benefit to the patient, their levels in drug


#### **Figure 3.**

*Comparison for the classification of residues of metal and elemental impurities in pharmaceutical products by requirements of EMA and ICH Q3D [9, 29, 30].*

products should be controlled within acceptable limits. Appropriate documentation demonstrating compliance for detailed risk assessment, screenings, and validation data for release methods must be conducted [9, 30, 34].

Recommended maximum acceptable concentration limits for the residues of metal catalysts or metal reagents that may be present in pharmaceutical products were issued earlier by EMA [29, 30]. Another classification of impurities, i.e., elemental impurities that the pharmaceutical industry needs to comply with is defined recently in ICH Q3D [9]. Comparison for these classifications of residues of metal or elemental impurities in pharmaceutical products defined by EMA and ICH was indicated as shown in **Figure 3**. Several significant difference of elemental safety concerns between EMA and ICH, such as Cr, As, Cd, Hg, Pb, etc., can be found.

#### **3. Strategies to establish analytical methods and acceptance criteria of PRIs and DRIs**

This chapter will be followed by a discussion of procedure to establish an analytical method and acceptance criteria of DRIs and PRIs.

Steps for the determination of potential degradation products, including a science-based risk assessment, can been addressed as below [11, 25]:


An integrated scheme in accordance with the requirements of ICH for the establishment of analytical methods and acceptance criteria of PRIs and DRIs is proposed as demonstrated in **Figure 4** [2, 3, 17, 22, 39, 40].

In general, when an unknown peak was found, no matter it was found in a stress or stability studies of API or drug product, the first step is to distinguish the classification of unknown impurity belongs to. Different regulatory requirements of the

**121**

**Figure 4.**

*Determination of Impurities in Pharmaceuticals: Why and How?*

management for different kinds of impurities, i.e., PRIs and DRIs are required to apply. For instance, requirements of ICH Q3B(R2) and Q1A(R2) request that impurities present in API need not be monitored or specified in the drug product unless they are also degradation products. Due to the probability of degradation during storage period and are likely to influence quality, safety, and/or efficacy, degradation impurities must be included into the plan of stability studies [39]. Meanwhile, degradation impurities can ultimately determine the expiration, retest, or shelf-life periods of API and drug products, by evaluating the intersection of extrapolationupper confidence limit and upper acceptance criterion of degradation product(s) [40]. Reporting threshold, identification threshold, and qualification threshold in the case of maximum daily dose ≤2 g/day of APIs administrated are illustrated in

Structure of impurities present in API at a level greater than (>) the identification threshold needs to be elucidated. An identified impurity content can be either

*Scheme to establish analytical methods and acceptance criteria of process-related impurities (PRIs) and degradation-related impurities (DRIs) according to the requirements of ICH guidelines [2, 3, 17, 22, 39, 40].*

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

**Figure 4** [17].

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

*Quality Management and Quality Control - New Trends and Developments*

products should be controlled within acceptable limits. Appropriate documentation demonstrating compliance for detailed risk assessment, screenings, and validation

*Comparison for the classification of residues of metal and elemental impurities in pharmaceutical products by* 

Recommended maximum acceptable concentration limits for the residues of metal catalysts or metal reagents that may be present in pharmaceutical products were issued earlier by EMA [29, 30]. Another classification of impurities, i.e., elemental impurities that the pharmaceutical industry needs to comply with is defined recently in ICH Q3D [9]. Comparison for these classifications of residues of metal or elemental impurities in pharmaceutical products defined by EMA and ICH was indicated as shown in **Figure 3**. Several significant difference of elemental safety concerns between EMA and ICH, such as Cr, As, Cd, Hg, Pb, etc., can be

**3. Strategies to establish analytical methods and acceptance criteria of** 

This chapter will be followed by a discussion of procedure to establish an

Steps for the determination of potential degradation products, including a

2.Accelerated stability studies or kinetically equivalent shorter term stability

An integrated scheme in accordance with the requirements of ICH for the establishment of analytical methods and acceptance criteria of PRIs and DRIs is

3.Validation/verification by long-term stability studies of both the drug substance

In general, when an unknown peak was found, no matter it was found in a stress or stability studies of API or drug product, the first step is to distinguish the classification of unknown impurity belongs to. Different regulatory requirements of the

analytical method and acceptance criteria of DRIs and PRIs.

proposed as demonstrated in **Figure 4** [2, 3, 17, 22, 39, 40].

science-based risk assessment, can been addressed as below [11, 25]:

data for release methods must be conducted [9, 30, 34].

*requirements of EMA and ICH Q3D [9, 29, 30].*

**120**

found.

**Figure 3.**

**PRIs and DRIs**

1.Stress studies of API.

and formulated drug product.

studies.

management for different kinds of impurities, i.e., PRIs and DRIs are required to apply. For instance, requirements of ICH Q3B(R2) and Q1A(R2) request that impurities present in API need not be monitored or specified in the drug product unless they are also degradation products. Due to the probability of degradation during storage period and are likely to influence quality, safety, and/or efficacy, degradation impurities must be included into the plan of stability studies [39]. Meanwhile, degradation impurities can ultimately determine the expiration, retest, or shelf-life periods of API and drug products, by evaluating the intersection of extrapolationupper confidence limit and upper acceptance criterion of degradation product(s) [40]. Reporting threshold, identification threshold, and qualification threshold in the case of maximum daily dose ≤2 g/day of APIs administrated are illustrated in **Figure 4** [17].

Structure of impurities present in API at a level greater than (>) the identification threshold needs to be elucidated. An identified impurity content can be either

#### **Figure 4.**

*Scheme to establish analytical methods and acceptance criteria of process-related impurities (PRIs) and degradation-related impurities (DRIs) according to the requirements of ICH guidelines [2, 3, 17, 22, 39, 40].*

determined by interpolation with calibration curve of reference material or calculated using the peak area of the main component, i.e., API. In contrast, unidentified impurity content can only be determined using the peak area of API, no matter they are specified or unspecified impurities. Impurities with specific acceptance criteria are referred to as specific impurities, including identified and unidentified impurities [2].

Before conducting method validation, all of the impurities shall be verified by spiked or known addition to demonstrate they do exist under the "real" storage conditions such as accelerated or long-term storage conditions. Otherwise, it may not be necessary to examine specifically for certain degradation products if they are not formed under the "real" storage conditions [11, 25, 39].

The method for technology transfer to QC laboratory, i.e., receiving unit (RU) must be a well-validated and stability-indicating method. A method fails to pass the criteria of validation or technology transfer, investigation to clarify the root cause(s) and revalidation shall be initiated and conducted by the originating unit (OU) and approved by quality unit (QU).

#### **4. Identification and validation of DRIs**

#### **4.1 Practice of kinetic study to distinguish PRIs and DRIs**

Algorithms for the identification and verification of DRIs are proposed as indicated in **Figure 5**. Degradation reaction kinetics can be represented by a linear regression curve on an arithmetic or logarithmic scale [39]. Meanwhile, nature of degradation relationship is determined by the reaction kinetic constants and can be accordingly used to distinguish whether an impurity is DRI or PRI compound (**Figure 5**).

One example regarding how to distinguish PRIs and DRIs by kinetic study was illustrated as demonstrated in **Figure 6**. Analysis by HPLC revealed that some impurities were existed in one of our products. Kinetic study helps us to distinguish the type of impurities.

Plots of the impurity formation concentration ([A] or Ln[A]) versus time can obtain rate constant, i.e., the slope of a reaction in straight line as arithmetic (i.e., k0) or logarithmic (i.e., k1) scale. Furthermore, correlation coefficient (r) of linear regression analysis indicates a perfect positive correlation (r = 1) or conversely, there is no relationship between the two variables (r = 0).

The slopes and correlation coefficients of Pk#5, Pk#6, and Pk#7 indicated that they were not degradation-related products of API. But conversely, kinetic curves showed that Pk#1–4 and Pk#8 were degradation products. These results were also consistent with the findings of molecular weight results shown in LC-MS/MS (data not shown).

#### **4.2 Unknown impurity structure elucidation using LC-MS/MS**

As shown in **Figure 5**, the first step for structure elucidation is running full Q1 scans in both positive ion mode and negative ion mode to locate the m/z of parent peak. In this step, sample solution is typically introduced directly into mass spectrometer (MS) at a flow rate of 10 μL/min using a syringe pump. However, since dimer or oligomer may also be one of the potential impurities, range of Q1 scan shall be as wide as possible, e.g., to mass number of 1000–1200 at least.

Carefully compare the difference of mass-to-charge (∆m/z) numbers between experimental and nominal values of parent (molecular) peak as well as their stable isotope distribution patterns and natural abundances. Previous study for the

**123**

of ECD (not [ECD+H]<sup>+</sup>

**Figure 5.**

pathways [24, 25].

*Determination of Impurities in Pharmaceuticals: Why and How?*

elucidation of degradation pathways of ethyl cysteinate dimer (ECD), a significant ∆m/z value of −2 in Q1 scan between experimental result (m/z = 323.60) and nominal result (m/z = 325.46) of parent peak was found and indicating that an

*Algorithms for the identification and verification of API-related degradation impurities (DRIs).*

Repeat the product ion scans, precursor ion scans, and neutral loss scans of API to establish its collision-activated dissociation (CID) fragmentation database, including the optimal CID energies of each fragment and multiple reaction monitoring (MRM) pairs. Propose the promising structures of CID fragments and fragmentation pathways of API, accordingly. Provide the comparison of ∆m/z results between experimental and nominal values for each peak, which is related to the fragmentation to verify the reliability of proposed fragments and fragmentation

) in aqueous solution before labeling of radioisotope, i.e.,

, was the prominent form

intramolecular disulfide (S-S) product, i.e., [ECDS-S+H]+

technetium-99m for i.v. injection (**Figure 7**) [25].

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

#### **Figure 5.**

*Quality Management and Quality Control - New Trends and Developments*

not formed under the "real" storage conditions [11, 25, 39].

**4.1 Practice of kinetic study to distinguish PRIs and DRIs**

there is no relationship between the two variables (r = 0).

**4.2 Unknown impurity structure elucidation using LC-MS/MS**

shall be as wide as possible, e.g., to mass number of 1000–1200 at least.

(OU) and approved by quality unit (QU).

**4. Identification and validation of DRIs**

determined by interpolation with calibration curve of reference material or calculated using the peak area of the main component, i.e., API. In contrast, unidentified impurity content can only be determined using the peak area of API, no matter they are specified or unspecified impurities. Impurities with specific acceptance criteria are referred to as specific impurities, including identified and unidentified impurities [2]. Before conducting method validation, all of the impurities shall be verified by spiked or known addition to demonstrate they do exist under the "real" storage conditions such as accelerated or long-term storage conditions. Otherwise, it may not be necessary to examine specifically for certain degradation products if they are

The method for technology transfer to QC laboratory, i.e., receiving unit (RU) must be a well-validated and stability-indicating method. A method fails to pass the criteria of validation or technology transfer, investigation to clarify the root cause(s) and revalidation shall be initiated and conducted by the originating unit

Algorithms for the identification and verification of DRIs are proposed as indicated in **Figure 5**. Degradation reaction kinetics can be represented by a linear regression curve on an arithmetic or logarithmic scale [39]. Meanwhile, nature of degradation relationship is determined by the reaction kinetic constants and can be accordingly used to distinguish whether an impurity is DRI or PRI compound

One example regarding how to distinguish PRIs and DRIs by kinetic study was illustrated as demonstrated in **Figure 6**. Analysis by HPLC revealed that some impurities were existed in one of our products. Kinetic study helps us to distinguish

Plots of the impurity formation concentration ([A] or Ln[A]) versus time can obtain rate constant, i.e., the slope of a reaction in straight line as arithmetic (i.e., k0) or logarithmic (i.e., k1) scale. Furthermore, correlation coefficient (r) of linear regression analysis indicates a perfect positive correlation (r = 1) or conversely,

The slopes and correlation coefficients of Pk#5, Pk#6, and Pk#7 indicated that they were not degradation-related products of API. But conversely, kinetic curves showed that Pk#1–4 and Pk#8 were degradation products. These results were also consistent with the findings of molecular weight results shown in LC-MS/MS (data

As shown in **Figure 5**, the first step for structure elucidation is running full Q1 scans in both positive ion mode and negative ion mode to locate the m/z of parent peak. In this step, sample solution is typically introduced directly into mass spectrometer (MS) at a flow rate of 10 μL/min using a syringe pump. However, since dimer or oligomer may also be one of the potential impurities, range of Q1 scan

Carefully compare the difference of mass-to-charge (∆m/z) numbers between experimental and nominal values of parent (molecular) peak as well as their stable isotope distribution patterns and natural abundances. Previous study for the

**122**

(**Figure 5**).

not shown).

the type of impurities.

*Algorithms for the identification and verification of API-related degradation impurities (DRIs).*

elucidation of degradation pathways of ethyl cysteinate dimer (ECD), a significant ∆m/z value of −2 in Q1 scan between experimental result (m/z = 323.60) and nominal result (m/z = 325.46) of parent peak was found and indicating that an intramolecular disulfide (S-S) product, i.e., [ECDS-S+H]+ , was the prominent form of ECD (not [ECD+H]<sup>+</sup> ) in aqueous solution before labeling of radioisotope, i.e., technetium-99m for i.v. injection (**Figure 7**) [25].

Repeat the product ion scans, precursor ion scans, and neutral loss scans of API to establish its collision-activated dissociation (CID) fragmentation database, including the optimal CID energies of each fragment and multiple reaction monitoring (MRM) pairs. Propose the promising structures of CID fragments and fragmentation pathways of API, accordingly. Provide the comparison of ∆m/z results between experimental and nominal values for each peak, which is related to the fragmentation to verify the reliability of proposed fragments and fragmentation pathways [24, 25].

**Figure 6.** *Kinetic study of impurities formation by conducting stress studies to distinguish DRIs and PRIs.*

#### **Figure 7.**

*Structures of (a) ethyl cysteinate dimer (ECD), (b) intramolecular disulfide (S-S) product of ECD, i.e., ECDS-S, and (c) intermolecular dimer of ECD and reducing agent (SnCl2), i.e., Sn(ECD)2 (DP#4) [25].*

Linear relationship within dynamic ranges for the quantitation of MRM pairs, i.e., correlation coefficients (r = 1) between precursor ions and product ions is another indication to verify high stability and reproducibility of fragmentation in CID conditions of tandem MS [24, 25].

Before using the MRM pairs for impurity scanning, interference of fragments generated from background, matrix, or contaminants such as plasticizers present in the solvents and mobile phase must be verified. Plasticizers, e.g., di(2-ethylhexyl) phthalate (DEHP) are one of the most common contaminants in organic solvents, including acetonitrile and alcohol [41].

Repeat the same procedures mentioned above in **Figure 5** to obtain a comprehensive information of fragments for any available intermediates and degradation products which are received from synthetic division, from contract manufacturing organization (CMO), from a stress study, or stability study sample conducted by the R&D team.

**125**

verification.

*Determination of Impurities in Pharmaceuticals: Why and How?*

1.Step 1: According to the CID fragments of API, intermediates, or/and degradation products, a list of potential core fragments, which may be related to the

3.Step 3: Conduct the precursor ion scans together with function of informationdependent acquisition (IDA), where CID is automatically performed on the two highest intensity MS peaks to find the possible precursor ions containing

4.Step 4: Perform the reliability assessment by analysis commercial batches or long-term/accelerated stability samples to verify the identification results of

One preliminary study was illustrated as shown in **Figure 8** can be used to detail

A total of five potential core fragments, coupled with the experience accumulated by degradation products that may be produced by similar chemical structures and prediction of relevant (bio-) transformations reactions under storage conditions, such as oxidation (+O, +2O), dehydration (−H2O, −2(H2O)), remove of carbon dioxide, and remove of acetic acid, a set of MRM pairs for scanning is

Conduct the precursor ion scans by coupled with the IDA function for automatic performing collision on the two highest intensity MS peaks in the targeting regions of HPLC (Step 3). (Note: IDA is a build-in function of API 4000 QTrap (AB Sciex) for conducting an automatic collision on the highest intensity peak(s) scan.)

In addition to the methods mentioned above, i.e., kinetic study and difference of mass-to-charge (∆m/z) between experimental and nominal results, three other evaluation methods to verify the reliability of the identification results are available: including verification by real samples, by stable isotope distribution patterns, and

Investigation results of unknown degradation product(s) must be verified by the "real samples", i.e., commercial batches or long-term/accelerated stability studies samples. Verification of reliability is achieved by comparison the difference of retention time (tR), MRM pairs, and stable isotope distribution patterns between real samples and stress study samples. If it is available, purified or enrichment sample of impurity can be spiked into a real sample for further

2.Verification by stable isotope distribution patterns or natural abundances

the algorithms of **Figure 5**. Core fragment of m/z 243 was found in the MS/MS study of API. In the meantime, four potential extending core fragments, i.e., m/z 183, m/z 185, m/z 197, and m/z 199 were obtained by the MS/MS studies of interme-

2.Step 2: Predict a set of potential/extending MRM pairs in line with the list obtained in step 1 and then coupled it with the relevant (bio-) transformations under the storage conditions of APIs/drug products for conducting MS/MS

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

scans.

step 3.

established (Step 2).

by mass balance.

1.Verification by real samples

unknown component(s) is proposed.

core fragments established in step 2.

diate and degradation product (Step 1).

**4.3 Verification of degradation products (step 4)**

Steps for the determination of impurities related to degradation of API are illustrated as follows:

*Quality Management and Quality Control - New Trends and Developments*

Linear relationship within dynamic ranges for the quantitation of MRM pairs, i.e., correlation coefficients (r = 1) between precursor ions and product ions is another indication to verify high stability and reproducibility of fragmentation in

*Structures of (a) ethyl cysteinate dimer (ECD), (b) intramolecular disulfide (S-S) product of ECD, i.e., ECDS-S, and (c) intermolecular dimer of ECD and reducing agent (SnCl2), i.e., Sn(ECD)2 (DP#4) [25].*

*Kinetic study of impurities formation by conducting stress studies to distinguish DRIs and PRIs.*

Before using the MRM pairs for impurity scanning, interference of fragments generated from background, matrix, or contaminants such as plasticizers present in the solvents and mobile phase must be verified. Plasticizers, e.g., di(2-ethylhexyl) phthalate (DEHP) are one of the most common contaminants in organic solvents,

Repeat the same procedures mentioned above in **Figure 5** to obtain a comprehensive information of fragments for any available intermediates and degradation products which are received from synthetic division, from contract manufacturing organization (CMO), from a stress study, or stability study sample conducted by the

Steps for the determination of impurities related to degradation of API are

CID conditions of tandem MS [24, 25].

including acetonitrile and alcohol [41].

**124**

R&D team.

**Figure 6.**

**Figure 7.**

illustrated as follows:


One preliminary study was illustrated as shown in **Figure 8** can be used to detail the algorithms of **Figure 5**. Core fragment of m/z 243 was found in the MS/MS study of API. In the meantime, four potential extending core fragments, i.e., m/z 183, m/z 185, m/z 197, and m/z 199 were obtained by the MS/MS studies of intermediate and degradation product (Step 1).

A total of five potential core fragments, coupled with the experience accumulated by degradation products that may be produced by similar chemical structures and prediction of relevant (bio-) transformations reactions under storage conditions, such as oxidation (+O, +2O), dehydration (−H2O, −2(H2O)), remove of carbon dioxide, and remove of acetic acid, a set of MRM pairs for scanning is established (Step 2).

Conduct the precursor ion scans by coupled with the IDA function for automatic performing collision on the two highest intensity MS peaks in the targeting regions of HPLC (Step 3). (Note: IDA is a build-in function of API 4000 QTrap (AB Sciex) for conducting an automatic collision on the highest intensity peak(s) scan.)

#### **4.3 Verification of degradation products (step 4)**

In addition to the methods mentioned above, i.e., kinetic study and difference of mass-to-charge (∆m/z) between experimental and nominal results, three other evaluation methods to verify the reliability of the identification results are available: including verification by real samples, by stable isotope distribution patterns, and by mass balance.

1.Verification by real samples

Investigation results of unknown degradation product(s) must be verified by the "real samples", i.e., commercial batches or long-term/accelerated stability studies samples. Verification of reliability is achieved by comparison the difference of retention time (tR), MRM pairs, and stable isotope distribution patterns between real samples and stress study samples. If it is available, purified or enrichment sample of impurity can be spiked into a real sample for further verification.

2.Verification by stable isotope distribution patterns or natural abundances

#### **Figure 8.**

*Step for the establishment of potential extending core fragments, conduct of product ions screening with transformation/IDA function, and validation/verification.*

Each element, like a fingerprint, has its own unique stable isotope distribution patterns and natural abundances. Occasionally, stable isotope distribution patterns or natural abundances are available as a unique tool for structure characterization.

Ten, two, and two of uncommon patterns in the MS spectra as shown in **Figure 9(a)**–**(c)** were clearly indicated in our structure identification of ethyl cysteinate dimer (ECD) cold kit, (R)-N-methyl-3-(2-bromophenoxy)-3 phenylpropanamine (MBPP), and methoxyisobutylisonitrile (sestamibi, or Cu(MIBI)4), respectively. These uncommon patterns were attributed to the contribution of stable isotope distributions of tin (Sn), bromine (Br), and copper (Cu), respectively.

When 7 major (or actually total 10) peaks are shown in the MS spectra, it may strongly mislead the works of structure elucidation as shown in **Figure 9(a)**. However, if it is available to know the presence of some special elements may present in impurity.

If it is able to presuppose that some special elements may contain in the structure, then it will be easier to elucidate the MS spectra. In other words, when pattern of MS spectra is significantly different from the normal CHO distribution, it may also indicate that a special element exists on the structure.

By comparing the natural abundance of 10 stable isotopes of tin and simulation MS spectra of a promising molecular formula, a series of metal complexes of tin can be verified. In the case for study of impurities in ECD kit, it was an ultimate and effective way to identify all of impurities containing Sn, i.e., DP#4, DP#5, DP#6, DP#6′, DP#6″, DP#7, DP#7′, DP#7″, and DP#8 [25]. Similar case was found in

**127**

**Figure 9.**

3.Verification by mass balance

*Determination of Impurities in Pharmaceuticals: Why and How?*

the structure determination of sestamibi as shown in **Figure 9(c)**. Coordination number (CN = 4) and core metal (Cu) in sestamibi can be clearly verified.

*Stable isotope distribution patterns and simulation of mass spectra of (a) Sn(ECD)2 (DP#4), (b) (R)-Nmethyl-3-(2-bromophenoxy)-3-phenylpropanamine (MBPP), and (c) methoxyisobutylisonitrile (sestamibi).*

When performing a stress study of API, one should determine content of API on each day by using a daily and freshly prepared calibration curve of API reference material, and interpolated within the validated dynamic range. The mass balance is

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

*Quality Management and Quality Control - New Trends and Developments*

Each element, like a fingerprint, has its own unique stable isotope distribution patterns and natural abundances. Occasionally, stable isotope distribution patterns or natural abundances are available as a unique tool for structure characterization. Ten, two, and two of uncommon patterns in the MS spectra as shown in **Figure 9(a)**–**(c)** were clearly indicated in our structure identification of ethyl cysteinate dimer (ECD) cold kit, (R)-N-methyl-3-(2-bromophenoxy)-3 phenylpropanamine (MBPP), and methoxyisobutylisonitrile (sestamibi, or Cu(MIBI)4), respectively. These uncommon patterns were attributed to the contribution of stable isotope distributions of tin (Sn), bromine (Br), and cop-

*Step for the establishment of potential extending core fragments, conduct of product ions screening with* 

When 7 major (or actually total 10) peaks are shown in the MS spectra, it may

If it is able to presuppose that some special elements may contain in the structure, then it will be easier to elucidate the MS spectra. In other words, when pattern of MS spectra is significantly different from the normal CHO distribution, it may

By comparing the natural abundance of 10 stable isotopes of tin and simulation MS spectra of a promising molecular formula, a series of metal complexes of tin can be verified. In the case for study of impurities in ECD kit, it was an ultimate and effective way to identify all of impurities containing Sn, i.e., DP#4, DP#5, DP#6, DP#6′, DP#6″, DP#7, DP#7′, DP#7″, and DP#8 [25]. Similar case was found in

strongly mislead the works of structure elucidation as shown in **Figure 9(a)**. However, if it is available to know the presence of some special elements may pres-

also indicate that a special element exists on the structure.

**126**

per (Cu), respectively.

*transformation/IDA function, and validation/verification.*

ent in impurity.

**Figure 8.**

#### **Figure 9.**

*Stable isotope distribution patterns and simulation of mass spectra of (a) Sn(ECD)2 (DP#4), (b) (R)-Nmethyl-3-(2-bromophenoxy)-3-phenylpropanamine (MBPP), and (c) methoxyisobutylisonitrile (sestamibi).*

the structure determination of sestamibi as shown in **Figure 9(c)**. Coordination number (CN = 4) and core metal (Cu) in sestamibi can be clearly verified.

#### 3.Verification by mass balance

When performing a stress study of API, one should determine content of API on each day by using a daily and freshly prepared calibration curve of API reference material, and interpolated within the validated dynamic range. The mass balance is

calculated by summation of the API and total impurity content. It is a tool to justify whether there are impurities unseparated (i.e., same retention time) or undetectable (e.g., without UV-visible chromophores). This topic and several major problems to cause poor mass balance have been detailed by Nussbaum et al. [42]

#### **5. Conclusions**

Management of impurities related to APIs in pharmaceutical products must be implemented in strict compliance with the regulatory requirements of pharmaceutical industry due to their quality and safety concerns. An integrated scheme in accordance with the regulatory requirements to establish analytical methods and acceptance criteria of process-related impurities (PRIs) and degradation-related impurities (DRIs) was presented, accordingly. Meanwhile, procedures for the identification and validation/verification of API-related DRIs were proposed. Validation or verification methods to evaluate the reliability of structure identification such as kinetic reactions, stress and stability studies, comparison of retention time(s) and ∆m/z between experimental and nominal values of targeting peaks, compatibility of MRM pairs with "real samples," stable isotope distribution patterns, and mass balance were demonstrated. Applying of the processes proposed in this article will help to ensure the reliability and quality of the impurity analytical results.

#### **Acknowledgements**

The authors would like to thank Dr. Shyh-Fong Chen, Mr. Chu-Huang Hsieh, Miss Jane-Yu Huang, Miss Pi-Lin Liu, and Mr. Yung-Hsuan Sung, Pharmaceutical Business Unit, Everlight Chemical Industrial Corporation (ECIC) for their helpful advice on the Regulatory Requirements in this chapter. The authors also appreciate Dr. Lai-Chuan Chang, Biotech Total Solutions Co., Ltd., Dr. Lee-Chung Men, Dr. Lie-Hang Shen, Dr. Mei-Hsiu Liao, Miss Yi-Chih Hsia, and Mr. Chang-Yung Su, Institute of Nuclear Energy Research (INER) for their great supporting on the radiopharmaceutical and analytical works.

#### **Author details**

Kung-Tien Liu1 \* and Chien-Hsin Chen<sup>2</sup>

1 Pharmaceutical Business Unit, Everlight Chemical Industrial Corporation (ECIC), Taipei, Taiwan

2 Everlight Chemical Industrial Corporation (ECIC), Taipei, Taiwan

\*Address all correspondence to: kungtien@ecic.com.tw

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**129**

2014

2009

*Determination of Impurities in Pharmaceuticals: Why and How?*

of structure activity relationships (SAR) in toxicology. Toxicological Sciences.

[11] Kleinman MH, Elder D, Teasdale A, Mowery MD, McKeown AP, Baertschi SW. Strategies to address mutagenic impurities derived from degradation in drug substances and drug products.

Organic Process Research and Development. DOI: 10.1021/acs.

[12] Wasylaschuk WR, Harmon PA, Wagner G, Harman AB, Templeton AC, Xu H, et al. Evaluation of hydroperoxides in common pharmaceutical excipients. Journal of Pharmaceutical Sciences. 2007;**96**(1):106-116. DOI: 10.1002/

[13] Prachi S, Komal C, Priti MJ. Influence of peroxide impurities in povidone on the stability of selected β-blockers with the help of HPLC. AAPS

PharmSciTech. 2017;**18**(7). DOI: 10.1208/s12249-017-0716-2

[15] Kiehl D. Characterization of Extractables and Leachables Associated

with Pharmaceutically Relevant Materials: Case Studies Outlining Analytical Approaches, Challenges and Examples. Indianapolis, IN, USA: Eli Lilly & Company. http:// apps.thermoscientific.com/media/ SID/LSMS/PDF/LSMSUsersMtg/ Indianapolis/DKiehl\_Thermo\_User\_

[16] Müller L, Mauthe RJ, Riley CM, Andino MM, De Antonis D, Beels C, et al. A rationale for determining, testing, and controlling specific

Meeting\_Seminar.pdf

[14] Fathima N, Mamatha T, Qureshi HK, Anitha N, Rao JV. Drug-excipient interaction and its importance in dosage form development. Journal of Applied Pharmaceutical Science. 2011;**1**(6):66-71

2000;**56**(1):8-17

oprd.5b00091

jps.20726

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

[1] USP Chapters <1086> Impurities in drug substances and drug products. USP 41. The United States Pharmacopeial

Convention. August 1, 2018

2006

**References**

[2] ICH Harmonised Tripartite Guideline. Impurities in new drug substances. Q3A(R2). ICH. 25 October

[3] ICH Harmonised Tripartite Guideline. Impurities in new drug products. Q3B(R2). ICH. 2 June 2006

[4] Crowley P, Martini LG. Drugexcipient interactions. Pharmaceutical

[5] Bharate SS, Bharate SB, Bajaj AN. Interactions and incompatibilities of pharmaceutical excipients with active pharmaceutical ingredients: A comprehensive review. Journal of Excipients and Food Chemicals.

[6] Hotha KK, Roychowdhury S, Subramanian V. Drug-excipient

of drug degradation pathways. American Journal of Analytical Chemistry. 2016;**7**:107-140

[8] ICH Harmonised Tripartite Guideline. Impurities: Guideline for Residual Solvents. Q3C(R6).

[9] ICH Harmonised Tripartite Guideline. Guideline for Elemental Impurities. Q3D. ICH. 16 December

[10] McKinney JD, Richard A, Waller C, Newman MC, Gerberick F. The practice

ICH. October 20, 2016

interactions: Case studies and overview

[7] FDA Guidance. ANDAs: Impurities in Drug Substances. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA); June

Technology. 2001;**13**:26-34

2010;**1**(3):3-26

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

#### **References**

*Quality Management and Quality Control - New Trends and Developments*

calculated by summation of the API and total impurity content. It is a tool to justify whether there are impurities unseparated (i.e., same retention time) or undetectable (e.g., without UV-visible chromophores). This topic and several major problems to cause poor mass balance have been detailed by Nussbaum et al. [42]

Management of impurities related to APIs in pharmaceutical products must be implemented in strict compliance with the regulatory requirements of pharmaceutical industry due to their quality and safety concerns. An integrated scheme in accordance with the regulatory requirements to establish analytical methods and acceptance criteria of process-related impurities (PRIs) and degradation-related impurities (DRIs) was presented, accordingly. Meanwhile, procedures for the identification and validation/verification of API-related DRIs were proposed. Validation or verification methods to evaluate the reliability of structure identification such as kinetic reactions, stress and stability studies, comparison of retention time(s) and ∆m/z between experimental and nominal values of targeting peaks, compatibility of MRM pairs with "real samples," stable isotope distribution patterns, and mass balance were demonstrated. Applying of the processes proposed in this article will

help to ensure the reliability and quality of the impurity analytical results.

The authors would like to thank Dr. Shyh-Fong Chen, Mr. Chu-Huang Hsieh, Miss Jane-Yu Huang, Miss Pi-Lin Liu, and Mr. Yung-Hsuan Sung, Pharmaceutical Business Unit, Everlight Chemical Industrial Corporation (ECIC) for their helpful advice on the Regulatory Requirements in this chapter. The authors also appreciate Dr. Lai-Chuan Chang, Biotech Total Solutions Co., Ltd., Dr. Lee-Chung Men, Dr. Lie-Hang Shen, Dr. Mei-Hsiu Liao, Miss Yi-Chih Hsia, and Mr. Chang-Yung Su, Institute of Nuclear Energy Research (INER) for their great supporting on the

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Pharmaceutical Business Unit, Everlight Chemical Industrial Corporation (ECIC),

2 Everlight Chemical Industrial Corporation (ECIC), Taipei, Taiwan

**128**

**Author details**

**Acknowledgements**

**5. Conclusions**

Kung-Tien Liu1

Taipei, Taiwan

provided the original work is properly cited.

\* and Chien-Hsin Chen<sup>2</sup>

radiopharmaceutical and analytical works.

\*Address all correspondence to: kungtien@ecic.com.tw

[1] USP Chapters <1086> Impurities in drug substances and drug products. USP 41. The United States Pharmacopeial Convention. August 1, 2018

[2] ICH Harmonised Tripartite Guideline. Impurities in new drug substances. Q3A(R2). ICH. 25 October 2006

[3] ICH Harmonised Tripartite Guideline. Impurities in new drug products. Q3B(R2). ICH. 2 June 2006

[4] Crowley P, Martini LG. Drugexcipient interactions. Pharmaceutical Technology. 2001;**13**:26-34

[5] Bharate SS, Bharate SB, Bajaj AN. Interactions and incompatibilities of pharmaceutical excipients with active pharmaceutical ingredients: A comprehensive review. Journal of Excipients and Food Chemicals. 2010;**1**(3):3-26

[6] Hotha KK, Roychowdhury S, Subramanian V. Drug-excipient interactions: Case studies and overview of drug degradation pathways. American Journal of Analytical Chemistry. 2016;**7**:107-140

[7] FDA Guidance. ANDAs: Impurities in Drug Substances. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA); June 2009

[8] ICH Harmonised Tripartite Guideline. Impurities: Guideline for Residual Solvents. Q3C(R6). ICH. October 20, 2016

[9] ICH Harmonised Tripartite Guideline. Guideline for Elemental Impurities. Q3D. ICH. 16 December 2014

[10] McKinney JD, Richard A, Waller C, Newman MC, Gerberick F. The practice of structure activity relationships (SAR) in toxicology. Toxicological Sciences. 2000;**56**(1):8-17

[11] Kleinman MH, Elder D, Teasdale A, Mowery MD, McKeown AP, Baertschi SW. Strategies to address mutagenic impurities derived from degradation in drug substances and drug products. Organic Process Research and Development. DOI: 10.1021/acs. oprd.5b00091

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[19] Kulkarni A, Kulkarni VA. Impurity: Pharma market and importance. MOJ Bioorganic & Organic Chemistry. 2017;**1**(4):128-129. DOI: 10.15406/ mojboc.2017.01.00023

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[24] Yang HH, Liu KT, Hsia YC, Chen WH, Chen CC, Men LC, et al. Development and validation of an HPLC method for determination of purity of Sn-ADAM, a novel precursor of serotonin transporter SPECT imaging agent I-123-ADAM. Journal of Food and Drug Analysis. 2010;**18**(5):307-318

[25] Liu KT, Lin YY, Hsia YC, Zhao JH, Su CY, Shen SY, et al. Study of degradation products and degradation pathways of ECD and its drug product, ECD kit. In: Akyar I, editor. Wide Spectra of Quality Control. Croatia: InTech; 2011. pp. 105-132. ISBN: 978-953-307-683-6

[26] Alsante KM, Ando A, Brown R, Ensing J, Hatajik TD, Kong W, et al. The role of degradant profiling in active pharmaceutical ingredients and drug products. Advanced Drug Delivery Reviews. 2007;**59**:29-37

[27] Holm R, Elder DP. Analytical advances in pharmaceutical impurity profiling. European Journal of Pharmaceutical Sciences. 2016;**87**:118-135

[28] EMA Guideline. Guideline on the Limits of Genotoxic Impurities. London: Committee for Medicinal Products for Human Use (CHMP), European Medicines Agency; 28 June 2006. EMEA/CHMP/QWP/251344/2006

[29] Committee for Medicinal Products for Human Use (CHMP). Guideline on the Specification Limits for Residues of Metal Catalysts. London: European Medicines Agency; January 2007. Doc. Ref. CPMP/SWP/QWP/4446/00 corr

[30] Committee for Medicinal Products for Human use (CHMP). Guideline on the Specification Limits for Residues of Metal Catalysts or Metal Reagents. London: European Medicines Agency; 21 February 2008. Doc. Ref. EMEA/ CHMP/SWP/4446/2000

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ICH Q1E. ICH; 6 February 2003

[41] de Zeeuw RA, Jonkman JHG, van Mansvelt FJW. Plasticizers as contaminants in high-purity solvents: A potential source of interference in biological analysis. Analytical Biochemistry. 1975;**67**(1):339-341

[42] Baertschi SW. Analytical methodologies for discovering and profiling degradation-related impurities. Trends in Analytical Chemistry. 2006;**25**(8):758-767

Guideline. Evaluation for stability data.

*DOI: http://dx.doi.org/10.5772/intechopen.83849*

[31] Committee for Medicinal Products for Human use (CHMP). Implementation Strategy of ICH Q3D Guideline. European Medicines Agency; 08 March 2017. EMA/CHMP/

[32] FDA Guidance. Genotoxic and Carcinogenic Impurities in Drug Substances and Products:

Recommended Approaches. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA);

[33] FDA Guidance. ANDAs: Impurities in Drug Products. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA);

Impurities in Drug Products. Center for Drug Evaluation and Research (CDER) and Center for Biologics Evaluation and Research (CBER), Food and Drug Administration (FDA); August 2018

[35] USP Chapters <232> Elemental Impurities—Limits. The United States

[36] USP Chapters <233> Elemental Impurities—Procedures. The United States Pharmacopeial Convention

[37] USP Chapters <467> Residual Solvents. The United States Pharmacopeial Convention

[38] WHO Annex 4. Guidelines on the quality, safety, and efficacy of biotherapeutic protein products prepared by recombinant DNA technology. WHO Technical Report Series No. 987. World Health

[39] ICH Harmonised Tripartite

Guideline. Stability testing of new drug substances and products. Q1A(R2).

Organization; 2014

ICH; 6 February 2003

Pharmacopeial Convention

[34] FDA Guidance. Elemental

QWP/115498/2017

December 2008

November 2010

*Determination of Impurities in Pharmaceuticals: Why and How? DOI: http://dx.doi.org/10.5772/intechopen.83849*

[31] Committee for Medicinal Products for Human use (CHMP). Implementation Strategy of ICH Q3D Guideline. European Medicines Agency; 08 March 2017. EMA/CHMP/ QWP/115498/2017

*Quality Management and Quality Control - New Trends and Developments*

[24] Yang HH, Liu KT, Hsia YC, Chen WH, Chen CC, Men LC, et al. Development and validation of an HPLC method for determination of purity of Sn-ADAM, a novel precursor of serotonin transporter SPECT imaging agent I-123-ADAM. Journal

of Food and Drug Analysis.

[25] Liu KT, Lin YY, Hsia YC, Zhao JH, Su CY, Shen SY, et al. Study of degradation products and degradation pathways of ECD and its drug product, ECD kit. In: Akyar I, editor. Wide Spectra of Quality Control. Croatia: InTech; 2011. pp. 105-132. ISBN:

[26] Alsante KM, Ando A, Brown R, Ensing J, Hatajik TD, Kong W, et al. The role of degradant profiling in active pharmaceutical ingredients and drug products. Advanced Drug Delivery

[27] Holm R, Elder DP. Analytical advances in pharmaceutical impurity profiling. European Journal of Pharmaceutical Sciences.

[28] EMA Guideline. Guideline on the Limits of Genotoxic Impurities. London: Committee for Medicinal Products for Human Use (CHMP), European Medicines Agency; 28 June 2006. EMEA/CHMP/QWP/251344/2006

[29] Committee for Medicinal Products for Human Use (CHMP). Guideline on the Specification Limits for Residues of Metal Catalysts. London: European Medicines Agency; January 2007. Doc. Ref. CPMP/SWP/QWP/4446/00 corr

[30] Committee for Medicinal Products for Human use (CHMP). Guideline on the Specification Limits for Residues of Metal Catalysts or Metal Reagents. London: European Medicines Agency; 21 February 2008. Doc. Ref. EMEA/

CHMP/SWP/4446/2000

2010;**18**(5):307-318

978-953-307-683-6

Reviews. 2007;**59**:29-37

2016;**87**:118-135

impurities in pharmaceuticals that possess potential for genotoxicity. Regulatory Toxicology and Pharmacology. 2006;**44**(3): 198-211. DOI: 10.1016/j. yrtph.2005.12.001

[17] Jacobson-Kram D, McGovern T. Toxicological overview of impurities in pharmaceutical products. Advanced Drug Delivery Reviews. 2007;**59**:

[18] Kelce WR, Castle KE, Ndikum-Moffor FM, Patton LM. Drug substance and drug product impurities, now what? MOJ Toxicology. 2017;**3**(1):9-13. DOI:

[19] Kulkarni A, Kulkarni VA. Impurity: Pharma market and importance. MOJ Bioorganic & Organic Chemistry. 2017;**1**(4):128-129. DOI: 10.15406/

[20] Bauer M, de Leede L, Van Der Waart M. Purity as an issue in pharmaceutical research and development. European Journal of Pharmaceutical Sciences.

[21] ICH Guideline. Assessment and control of DNA reactive (mutagenic) impurities in pharmaceuticals to limit potential carcinogenic risk. M7(R1).

[22] ICH Harmonised Tripartite Guideline. Validation of analytical procedures: Text and methodology. Q2(R1). ICH. November 2005

10.1208/s12249-013-0047-x

[23] Alsante KM, Huynh-Ba K, Baertschi SW, Reed RA, Landis MS, Kleinman MH, et al. Recent trends in product development and regulatory issues on impurities in active pharmaceutical ingredient (API) and drug products. Part 1: Predicting degradation related impurities and impurity considerations for pharmaceutical dosage forms. AAPS PharmSciTech. 2014;**15**(1). DOI:

10.15406/mojt.2017.03.00043

mojboc.2017.01.00023

1998;**6**:331-335

ICH. 31 March 2017

38-42

**130**

[32] FDA Guidance. Genotoxic and Carcinogenic Impurities in Drug Substances and Products: Recommended Approaches. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA); December 2008

[33] FDA Guidance. ANDAs: Impurities in Drug Products. Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA); November 2010

[34] FDA Guidance. Elemental Impurities in Drug Products. Center for Drug Evaluation and Research (CDER) and Center for Biologics Evaluation and Research (CBER), Food and Drug Administration (FDA); August 2018

[35] USP Chapters <232> Elemental Impurities—Limits. The United States Pharmacopeial Convention

[36] USP Chapters <233> Elemental Impurities—Procedures. The United States Pharmacopeial Convention

[37] USP Chapters <467> Residual Solvents. The United States Pharmacopeial Convention

[38] WHO Annex 4. Guidelines on the quality, safety, and efficacy of biotherapeutic protein products prepared by recombinant DNA technology. WHO Technical Report Series No. 987. World Health Organization; 2014

[39] ICH Harmonised Tripartite Guideline. Stability testing of new drug substances and products. Q1A(R2). ICH; 6 February 2003

[40] ICH Harmonised Tripartite Guideline. Evaluation for stability data. ICH Q1E. ICH; 6 February 2003

[41] de Zeeuw RA, Jonkman JHG, van Mansvelt FJW. Plasticizers as contaminants in high-purity solvents: A potential source of interference in biological analysis. Analytical Biochemistry. 1975;**67**(1):339-341

[42] Baertschi SW. Analytical methodologies for discovering and profiling degradation-related impurities. Trends in Analytical Chemistry. 2006;**25**(8):758-767

## *Edited by Paulo Pereira and Sandra Xavier*

Quality management (QM) practices are the basis for the successful implementation and maintenance of any QM system. Quality control (QC) is identified as a QM component. Therefore, QM effectiveness is dependent on the QC strategy. QC practice is more or less complex depending on the type of production. The book is focused on new trends and developments in QM and QC in several types of industries from a worldwide perspective. Its content has been organized into two sections and seven chapters written by well-recognized researchers worldwide. Several approaches are debated based on sample traceability, analytical method validation, required parameters, class of exponential regression-type estimators of the population means, determination of impurities, viewpoints, and case studies.

Published in London, UK © 2019 IntechOpen © industryview / iStock

Quality Management and Quality Control - New Trends and Developments

Quality Management

and Quality Control

New Trends and Developments

*Edited by Paulo Pereira and Sandra Xavier*