**4. Preparation of samples**

In order to obtain high quality infrared spectra, a proper method should be selected for sample preparation according to the characteristics of the sample. Close attention should be paid to the following in sample preparation: 1) Purified and separated sample. IR spectrum of mixed sample will be shown in bands of various components and may mislead judgment for the sample. 2) Free of moisture. The infrared spectroscopy is very sensitive to moisture. If there is any trace of moisture in the sample, bands with intensive OH radical characteristic will be appeared near 3400cm-1, affecting the identification of N-H, C-H bonds. 3) Proper concentration and thickness of the sample. In good infrared spectra, most of the absorption bands have transmittance of between 20 to 80%. In especially low concentration or thin thickness, weak absorption bands and band of medium strength will disappear, resulting in inaccurate absorption spectrum. On the contrary, the excessive strong absorption will result in flat peak with no maximum value of the peak or indistinct double peaks.

#### **4.1 Solid sample preparation technology**

Common solid samples include polymer and some organic compounds. The following methods are usually adopted for sample preparation:


#### Sample Preparation

Put the fully grounded powder sample in the agate mortar, add 1-2 drops of medium by dropper and blend evenly. Use stainless steel spatula to scoop out the evenly grounded sample, paste it on a window slice, compress with another window slice to a proper thickness and then measure it.

Notes:

170 Macro to Nano Spectroscopy

infrared activity. The explanation of infrared spectrum of polymer must take into account the molecular chain structure and the aggregate structure of the concerned polymer. Different structural characteristics correspond to different absorption bands: ① absorption bands: reflects the chemical composition of polymer structural unit, connection type of monomers, branching or cross-linking and sequence distribution. ② Conformation bands: such bands are related to the certain conformation of some radical in the molecular chain and have different representations in different morphologies. ③ Stereoregularity bands: these bands are related to the structure of the molecular chain and are therefore identical in the various morphologies of the same high polymer. ④ Conformational regularity bands: these kinds of bands are generated as result of the mutual action of the adjacent radicals in the molecular chain. ⑤ Crystal bands: the bands are formed as a result of the interaction

In order to obtain high quality infrared spectra, a proper method should be selected for sample preparation according to the characteristics of the sample. Close attention should be paid to the following in sample preparation: 1) Purified and separated sample. IR spectrum of mixed sample will be shown in bands of various components and may mislead judgment for the sample. 2) Free of moisture. The infrared spectroscopy is very sensitive to moisture. If there is any trace of moisture in the sample, bands with intensive OH radical characteristic will be appeared near 3400cm-1, affecting the identification of N-H, C-H bonds. 3) Proper concentration and thickness of the sample. In good infrared spectra, most of the absorption bands have transmittance of between 20 to 80%. In especially low concentration or thin thickness, weak absorption bands and band of medium strength will disappear, resulting in inaccurate absorption spectrum. On the contrary, the excessive strong absorption will result

Common solid samples include polymer and some organic compounds. The following

1. Pressed halide disk method (KBr Pressed Disk Method), mix a quantitative amount of samples (accurately measured for quantitative analysis) And some ground and screened KBr powder in the agate mortar in proper proportion and pulverize them completely until there is no obvious particles in the blends. Please be noted: KBr requires the use of analytical reagent or higher. Qualified KBr should be no absorption in mid-infrared region. Moisture absorption will result in moisture absorption peak. In addition, KBr powder tends to absorb the vapor in the air and should be dried before use. Screen the KBr powder with 200-mesh sieve, then dried under 120°C and put the powder in the dryer for use. The temperature should not be too high(greater

Put the fully grounded powder sample in the agate mortar, add 1-2 drops of medium by dropper and blend evenly. Use stainless steel spatula to scoop out the evenly grounded

in flat peak with no maximum value of the peak or indistinct double peaks.

between the adjacent molecular chains in the crystal.

**4.1 Solid sample preparation technology** 

2. Paste Method Sample Preparation

methods are usually adopted for sample preparation:

than120°C), otherwise it will decompose (see spectra 1).

**4. Preparation of samples** 

All the media used in the method are organic matter and can absorb in certain range. The absorption positions of the media are as shown below:

Fig. 1. Absorption requirement of qualified KBr


Table 4. The absorption positions of the media

The IR spectra of above three media have complementary. Complete infrared spectrogram of the sample can be obtained by at least two media. In this consideration, the influence of the media spectrogram should be deducted from spectrum analysis of the sample to baseline.

3. Solution film casting method

Sample preparation method

Dissolve the sample in an appropriate volatile solvent to prepare a solution with concentration of around 2-5%, apply the solution evenly on the watch glass and glass sheet,

Application of Infrared Spectroscopy in Biomedical Polymer Materials 173

Yang Rui from Tsinghua University has made a detailed research and analysis(in 2011) as

**Thermoplastic resin:** dissolve flow casting film, hot-pressing film or dissolve coated tablet. **Thermosetting resin:** such as curing epoxy resin and phenolic resin. Use clean steel file to

**Mild cross-link polymer:** sample that only swells instead of dissolving in solvent. Grind with KBr in swelling (with solvent) condition, then dry the solvent and pulverize the tablet. **Fiber sample**: Filament with diameter of less than 10 microns can be neatly arranged (or be cut into piece) to determine the transmission spectra with KBr pellet. Filament with larger diameter or non-filament fiber should be entangled on the aluminum tablet or be squashed

Polymer Temperature

170 Nylon 11 220

terephthalate

terephthalate

/℃

290

250

/°C

PMMA 260 Polybutylene

PVC 190 Polybutylene

**4.2.1 Material of window slice used for organic liquid testing** 

suitable window slice material for testing organic liquid in middle infrared.

Low density polyethylene 150 Nylon 66 280 Polypropylene 200 Metaformaldehyde 190 Polystyrene 130 Makrolon 260

Nylon 6 250 Teflon 360

Figure 2 shows PMMA infrared spectrum from different sample preparation methods. The PMMA infrared spectrum from powder pulverized tablet and hot-pressing film are nearly same on wavenunbers, and slightly different on wave intensity. But there is another additional infrared eigen wave (at 760 cm-1) for PMMA infrared spectrum from solution film

KBr and NaCl are the most commonly used window slice materials used for determination of IR spectrum of the organic solution. But KBr is widely used than NaCl. KBr is the most

Rinse the KBr wafer immediately after testing. As KBr is non-dissolvable with in soluble, remove the organic solvent from the surface of the wafer by anhydrous ethanol instead of

Table 5. Reference Temperature for Hot-pressing Film of Common Polymers

below:

file sample powder and then use KBr pellet.

Polymer Temperature

casting method (chloroform resolving).

**4.2 Liquid sample preparation technology** 

clean water, then dry with crystal-tipped tissue.

for determination with ART.

High-density polyethylene

Low density linear polyethylene

or drop it directly on the infrared wafers (KBr, NaCl, BaF etc), then solvent volatilize to obtain sample film.

Application Scope: mainly used in sample analysis with both film-forming and solvent dissolving.

Notes:

The selection of solvent and the concentration of the sample prepared play an important role in obtain even and pure film.

Principle for Solvent Selection:

All solvents have infrared spectrum absorption band. Commonly used solvent oil include CCl4, CH Cl3, CS2 and n-hexane.

Select solvent with low boiling point instead of using solvent with high boiling point and strong polarity, otherwise, the film thickness will be uneven as result of the fast solvent volatilization.

The solubility of the sample in the solvent should be sufficient high. The solution concentration can be regulated.

4. Hot-press film making method

Hot-press device: composed of hydraulic membrane machine, heating die and temperature control device.

Hot-press temperature setup for various common polymers

Sample preparation method

Place a piece of aluminum foil in the core of the die, put the sample on the aluminum foil and then place another piece of aluminum foil on the sample; put on the upper module and then place the die on the tablet press. Control the pressure within 1000-3000Kpa/cm2. The heating temperature and time for pressing shall be controlled to the extent that there is no thermal decomposition or other chemical changes. After pressing for about 1min, take down the die from the hydraulic press (wear insulating glove to avoid burn), cool to room temperature and then unpack the die to take out the sample tablet. Reduce sample volume if the film is too thick. Reduce temperature if the film turns yellow or has bubbles. Uneven film is caused by low heating temperature, too short heating time or small pressure. Reselect film making condition to remake the film in case of any of the above circumstances.

Application Scope: applicable for non-oxidizing and non-degradable thermoplastic or inorganic polymer materials near the softening point or melting point.

Notes:

Select appropriate hot pressing temperature and pressing time according to the nature of the analyzde sample in order to obtain hot press film in line with infrared transmittance while not destroying structure performance of the sample. Take protective measure against burn when operating in high temperature.

General solid sampling technique can be used in the infrared analysis. However, improvement has been made in actual operation based on the features of the polymer. Mr.

or drop it directly on the infrared wafers (KBr, NaCl, BaF etc), then solvent volatilize to

Application Scope: mainly used in sample analysis with both film-forming and solvent

The selection of solvent and the concentration of the sample prepared play an important role

All solvents have infrared spectrum absorption band. Commonly used solvent oil include

Select solvent with low boiling point instead of using solvent with high boiling point and strong polarity, otherwise, the film thickness will be uneven as result of the fast solvent

The solubility of the sample in the solvent should be sufficient high. The solution

Hot-press device: composed of hydraulic membrane machine, heating die and temperature

Place a piece of aluminum foil in the core of the die, put the sample on the aluminum foil and then place another piece of aluminum foil on the sample; put on the upper module and then place the die on the tablet press. Control the pressure within 1000-3000Kpa/cm2. The heating temperature and time for pressing shall be controlled to the extent that there is no thermal decomposition or other chemical changes. After pressing for about 1min, take down the die from the hydraulic press (wear insulating glove to avoid burn), cool to room temperature and then unpack the die to take out the sample tablet. Reduce sample volume if the film is too thick. Reduce temperature if the film turns yellow or has bubbles. Uneven film is caused by low heating temperature, too short heating time or small pressure. Reselect

film making condition to remake the film in case of any of the above circumstances.

inorganic polymer materials near the softening point or melting point.

Application Scope: applicable for non-oxidizing and non-degradable thermoplastic or

Select appropriate hot pressing temperature and pressing time according to the nature of the analyzde sample in order to obtain hot press film in line with infrared transmittance while not destroying structure performance of the sample. Take protective measure against burn

General solid sampling technique can be used in the infrared analysis. However, improvement has been made in actual operation based on the features of the polymer. Mr.

obtain sample film.

in obtain even and pure film. Principle for Solvent Selection:

CCl4, CH Cl3, CS2 and n-hexane.

concentration can be regulated.

Sample preparation method

4. Hot-press film making method

when operating in high temperature.

Hot-press temperature setup for various common polymers

dissolving.

volatilization.

control device.

Notes:

Notes:

Yang Rui from Tsinghua University has made a detailed research and analysis(in 2011) as below:

**Thermoplastic resin:** dissolve flow casting film, hot-pressing film or dissolve coated tablet.

**Thermosetting resin:** such as curing epoxy resin and phenolic resin. Use clean steel file to file sample powder and then use KBr pellet.

**Mild cross-link polymer:** sample that only swells instead of dissolving in solvent. Grind with KBr in swelling (with solvent) condition, then dry the solvent and pulverize the tablet.

**Fiber sample**: Filament with diameter of less than 10 microns can be neatly arranged (or be cut into piece) to determine the transmission spectra with KBr pellet. Filament with larger diameter or non-filament fiber should be entangled on the aluminum tablet or be squashed for determination with ART.


Table 5. Reference Temperature for Hot-pressing Film of Common Polymers

Figure 2 shows PMMA infrared spectrum from different sample preparation methods. The PMMA infrared spectrum from powder pulverized tablet and hot-pressing film are nearly same on wavenunbers, and slightly different on wave intensity. But there is another additional infrared eigen wave (at 760 cm-1) for PMMA infrared spectrum from solution film casting method (chloroform resolving).
