**2. Description of methodologies**

162 Multivariate Analysis in Management, Engineering and the Sciences

signatures.

Explosives and Chemical Warfare Agents, as well as other chemical and biological threats in airports, in military environments, in government buildings and other public safety places. Raman Spectroscopy employs a non-invasive approach that provides high resolution and specificity. Some applications of IRS and RS includes lab based characterization studies as well as forensic field studies of organic and inorganic substances through their vibration

Optical Fiber Probes (OFP) have been employed in biomedical applications, in communications, in coupling instrumentation to sensing probes and other important modern applications. Moreover, their uses have been extended to excitation and detection of Raman and infrared signals [16, 20]. Fiber optics applications to Raman Spectroscopy can take advantage of a favorable excitation radiation distribution within the sample; allowing the use of higher laser power levels which, in turn, can yield an elevated signal-to-noise ratio (SNR) for a given experiment without increasing the risk of photo-damaging analytes [21, 22]. In 2011 Ramírez-Cedeño et al. utilized Optical Fiber Coupled Raman Spectroscopy (OFC-RS) to detect hazardous liquids concealed in commercial products [6]. They proved that an optical fiber coupled Raman probe was able to discriminate hazardous liquids inside consumer products from common drinks. Elliason et al. (2007) have also reported drug and

Recently infrared spectroscopy has shown progress in the use of more powerful IR sources, such as Quantum Cascade Lasers (QCL) by incorporating these devices in IR reflectance, IR transmission and even in IR microscopy applications [24]. QCL-based setups are being developed for in the field applications such as breath analysis, environmental research, airborne measurements, security applications, laser-based isotope ratio measurements, and many others. In particular, for security applications, optical methods are advantageous because of their capability for remote and standoff detection [14, 25, 26]. Due to improvements in QCL development, mid infrared lasers operating at room temperature with high output powers in the CW regime are commercially available and make it possible to set up a ruggedized system that allows sensing of explosives and others materials outside the laboratory and the ability to enter real world scenarios. With laser based standoff spectroscopy, the detection distance can be a few meters to tens of meters. Because of the inverse square dependence of light intensity, larger distances require high power, collimated light sources such as lasers. For homeland security applications such as detection of suicide

bombers or improvised explosive devices, a distance of 50-100 m is generally sufficient.

In this chapter we illustrate the usefulness of incorporating powerful statistical routines to all traditional chemistry disciplines: Chemometrics is the application of statistical tools to plan, execute and analyze experiments in chemistry. To illustrate the power of Chemometrics techniques to analyze experiments in chemistry we have chosen three case studies, all involving identification, quantification, discrimination and classification of chemical threats in different matrices from vibrational spectroscopy multivariate data.

In the first case study a remote Raman detection study was performed for quantification of HEM such as pentaerythritol tetranitrate (PETN) present in different mixtures. The remote

liquid explosives detection in concealed in colored plastic containers [23].

Explosives compounds employed in the studies illustrated were pentaerythritol tetranitrate (PETN) cyclotrimethylenetrinitramine (RDX), triacetone triperoxide (TATP), 2,4 dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT) were synthesized in the laboratory according to methods described by Urbanski [27] and pharmaceutical active compound: acetaminophen (APAP) was purchased from Aldrich-Sigma Chemical Co. (Milwaukee, WI). Powder mixtures were prepared employing the both compounds (PETN and APAP) mentioned above and the compositions of PETN in the mixtures was varied from 1 to 34% w/w. Components of the mixtures were carefully weighed and mixed using an agate mortar ensuring homogeneity throughout the sample with a total weight of 200 mg.

**Figure 1.** Commercial bottles (glass and plastic) used to TEP detection using Optical Fiber Coupled Raman spectroscopy.

Multivariate Analysis in Vibrational

Spectroscopy of Highly Energetic Materials and Chemical Warfare Agents Simulants 165

maximum energy/pulse of the laser at 532 nm was 25 mJ, and it operated at a repetition rate of 10 Hz. The pulse width was approximately 5-8 ns, and the beam divergence was less than 0.5 mrad. A gateable, intensified CCD detector (iStar ICCD camera, Model DH-720i-25F-03, Andor Technology, Belfast, Northern Ireland) was used as the photon detector. Andor Technology Solis software for spectroscopic, imaging and time-resolved studies was used for spectral data acquisition and processing from the intensified and gated CCD detector. Using this software, the data could be acquired in both imaging and spectroscopic modes. In this experiments, each mixture was placed into a stainless steel sample holder of 0.6 cm in diameter where 30 ft·lb of pressure was applied to generate a tablet. Remote Raman spectra of mixtures were measured at a target at telescope standoff distance of 10 m, in the Raman Shift region 450-3000 cm-1 using an pulsed laser operating at 532 nm excitation line with a constant energy of 25mJ/pulse (at head) and 100 pulses were applied to achieve spectra with good Signal to Noise. A total of 10 spectra were collected for each mixture acquiring around

**Figure 3.** General scheme of experiments using IR and Raman vibrational spectroscopy.

In the detection of TEP chemical warfare simulant in commercial bottles, Raman experiments were performed with a custom built setup (Figure 4) using the strong blue excitation line from an argon ion laser INNOVA 310/8 from Coherent, Inc. at 488.0 nm. The first strand of optical fiber (non-imaging, 600 µm diameter, model AL 1217, Ocean Optics, Inc.) as well as the second (200 µm diameter, model SR-OPT 8024, Andor Technologies Inc.) were used to couple the Raman probe to which a set of laser line filter (to clean satellite lines) and Semrock RazorEdge™ edge filter was used to filter the Rayleigh scattered light. An Andor Technologies spectrograph: Shamrock SR-303i (aperture: f/4; focal length: 303 mm; wavelength resolution: 0.1 nm or 4.2 cm-1 at the excitation wavelength) equipped with a 1200 grooves/mm grating was used to analyze the Stokes scattered light. A high performance, back thin illuminated CCD camera (Andor Technologies model # DU970N-

56 spectra in the specific Raman shift range.

**Figure 2.** Microscopic Views of PETN on travel baggage substrates; zoom used was 10x and 50x.

A chemical warfare agent simulant: (CWAS) triethyl phosphate 99% (TEP) from Acros Organics (New Jersey, USA) was used to demonstrate the detection and quantification capabilities of this kind of compound by Optical Fibers Coupled Raman spectroscopy. Several formulations were made with the stimulant in their commercial containers: Snapple® Kiwi-Strawberry (Snapple Group USA), Pepsi (PepsiCo Inc., USA), Mountain Dew® (PepsiCo Inc., USA), Heineken® (Mendez & Company, PR), Mott's apple juice® (Mott's LLP., Rye Brook, NY) , Leche Suiza® Low Fat Grade A (Suiza Dairy Corp., Puerto Rico) and Malta India® (PR Brewing Co., Mayaguez, PR). The containers can be seen in Figure 1.

For gas phase measurements of 2,4-DNT and TATP using infrared spectroscopy vapors were collected in a gas cell (10 cm long and 3.5 cm diameter) by slowly heating the sample to generate vapors. Finally, traces of PETN, TNT and RDX were placed on travel baggage surface with size of 1 in2. Figure 2 shows a view of how PETN was deposited on travel baggage substrates at different surface concentration. Figure 3 shows a summary the experiments carried out using vibrational spectroscopy techniques such as infrared and Raman. This figure shows the modalities used, the target tested and the chemometrics models utilized.

For detection of PETN mixed with APAP, Raman spectra of mixtures were acquired by employing a Remote Raman system. This system has been described in detail previously [16]. The prototype was modified using a Headwall Photonics Raman Explorer™ spectrograph with optical layout for 532 nm (Headwall Photonics, Inc.) instead of the Andor spectrometer. The remote Raman system consisted of a MEADE ETX-125 Maksutov-Cassegrain telescope (125 mm clear aperture, 1900 mm focal length f /15). The reflecting collector was coupled to the Raman spectrometer with non-imaging, 200 m diameter optical fiber (model SR-OPT-8024, Andor Technology, Belfast, Northern Ireland). A frequency-doubled 532 nm Nd:YAG pulsed laser system (Quanta Ray INDI Series, Newport-Spectra Physics, Mountain View, CA) was used as the excitation source. The maximum energy/pulse of the laser at 532 nm was 25 mJ, and it operated at a repetition rate of 10 Hz. The pulse width was approximately 5-8 ns, and the beam divergence was less than 0.5 mrad. A gateable, intensified CCD detector (iStar ICCD camera, Model DH-720i-25F-03, Andor Technology, Belfast, Northern Ireland) was used as the photon detector. Andor Technology Solis software for spectroscopic, imaging and time-resolved studies was used for spectral data acquisition and processing from the intensified and gated CCD detector. Using this software, the data could be acquired in both imaging and spectroscopic modes. In this experiments, each mixture was placed into a stainless steel sample holder of 0.6 cm in diameter where 30 ft·lb of pressure was applied to generate a tablet. Remote Raman spectra of mixtures were measured at a target at telescope standoff distance of 10 m, in the Raman Shift region 450-3000 cm-1 using an pulsed laser operating at 532 nm excitation line with a constant energy of 25mJ/pulse (at head) and 100 pulses were applied to achieve spectra with good Signal to Noise. A total of 10 spectra were collected for each mixture acquiring around 56 spectra in the specific Raman shift range.

164 Multivariate Analysis in Management, Engineering and the Sciences

Blank 10x

Blank 50x

**Figure 2.** Microscopic Views of PETN on travel baggage substrates; zoom used was 10x and 50x.

Brewing Co., Mayaguez, PR). The containers can be seen in Figure 1.

models utilized.

A chemical warfare agent simulant: (CWAS) triethyl phosphate 99% (TEP) from Acros Organics (New Jersey, USA) was used to demonstrate the detection and quantification capabilities of this kind of compound by Optical Fibers Coupled Raman spectroscopy. Several formulations were made with the stimulant in their commercial containers: Snapple® Kiwi-Strawberry (Snapple Group USA), Pepsi (PepsiCo Inc., USA), Mountain Dew® (PepsiCo Inc., USA), Heineken® (Mendez & Company, PR), Mott's apple juice® (Mott's LLP., Rye Brook, NY) , Leche Suiza® Low Fat Grade A (Suiza Dairy Corp., Puerto Rico) and Malta India® (PR

0.51 µg/cm2 50x

0.51 µ g/cm 2 10x

8.53 µg/cm2 10x

8.53 µg/cm2 50x

For gas phase measurements of 2,4-DNT and TATP using infrared spectroscopy vapors were collected in a gas cell (10 cm long and 3.5 cm diameter) by slowly heating the sample to generate vapors. Finally, traces of PETN, TNT and RDX were placed on travel baggage surface with size of 1 in2. Figure 2 shows a view of how PETN was deposited on travel baggage substrates at different surface concentration. Figure 3 shows a summary the experiments carried out using vibrational spectroscopy techniques such as infrared and Raman. This figure shows the modalities used, the target tested and the chemometrics

For detection of PETN mixed with APAP, Raman spectra of mixtures were acquired by employing a Remote Raman system. This system has been described in detail previously [16]. The prototype was modified using a Headwall Photonics Raman Explorer™ spectrograph with optical layout for 532 nm (Headwall Photonics, Inc.) instead of the Andor spectrometer. The remote Raman system consisted of a MEADE ETX-125 Maksutov-Cassegrain telescope (125 mm clear aperture, 1900 mm focal length f /15). The reflecting collector was coupled to the Raman spectrometer with non-imaging, 200 m diameter optical fiber (model SR-OPT-8024, Andor Technology, Belfast, Northern Ireland). A frequency-doubled 532 nm Nd:YAG pulsed laser system (Quanta Ray INDI Series, Newport-Spectra Physics, Mountain View, CA) was used as the excitation source. The

**Figure 3.** General scheme of experiments using IR and Raman vibrational spectroscopy.

In the detection of TEP chemical warfare simulant in commercial bottles, Raman experiments were performed with a custom built setup (Figure 4) using the strong blue excitation line from an argon ion laser INNOVA 310/8 from Coherent, Inc. at 488.0 nm. The first strand of optical fiber (non-imaging, 600 µm diameter, model AL 1217, Ocean Optics, Inc.) as well as the second (200 µm diameter, model SR-OPT 8024, Andor Technologies Inc.) were used to couple the Raman probe to which a set of laser line filter (to clean satellite lines) and Semrock RazorEdge™ edge filter was used to filter the Rayleigh scattered light. An Andor Technologies spectrograph: Shamrock SR-303i (aperture: f/4; focal length: 303 mm; wavelength resolution: 0.1 nm or 4.2 cm-1 at the excitation wavelength) equipped with a 1200 grooves/mm grating was used to analyze the Stokes scattered light. A high performance, back thin illuminated CCD camera (Andor Technologies model # DU970N-

UVB) with quantum efficiencies of 90% (200 cm-1) to 95% (3600 cm-1) served as light detector (Figure 4) and calibration was performed using cyclohexane. Detection was performed with a light source in order to be carried out in the high-background environment conditions. In this experiment, six different bottle materials: clear-glass, green-glass, brown-glass, clearplastic, white-plastic and green-plastic were used to measure the amount of simulant (triethyl phosphate) within the container. Mixtures ranged from 0% to 100% (v/v) of simulant and water, simulant and commercial beverage product were analyzed.

Multivariate Analysis in Vibrational

Spectroscopy of Highly Energetic Materials and Chemical Warfare Agents Simulants 167

The IR equipment used for the experiments was a model IFS 66v/S interferometer (Bruker Optics, Billerica, MA). For the experiments described, the system was equipped with a DTGS detector and a potassium bromide (KBr) beamsplitter. A spectroscopic measurement averaged 20 scans at a resolution of 4 cm-1 using OPUS Version 4.2 software in the range of 7500 – 400 cm-1. Target chemicals were TATP, 2,4-DNT and 2,4,6-TNT. Second, an EM-27 Open Path FT-IR interferometer (Bruker Optics, Billerica, MA) was used to obtain the IR spectral information of gas phase TATP samples with a (TE) cooled MCT detector. Third: Quantum Cascade Laser (QCL) based dispersive IR spectrometer LaserTune™ (Block Engineering, Marlborough, MA) was used to obtain the IR spectral information of TATP samples. An Agilent 6890 gas chromatograph (GC) coupled to an Agilent 5893 mass selective detector (MSD) with a capillary column: HP-5 MS 5% phenyl methyl siloxane, Length: 30.0 m, 250.0 µm in diameter and 0.25 µm of film thickness was used for detecting

Figure 5 shows a schematic diagram of the experimental setup used in the investigation. Samples of 100-300 µg/cm2 of explosives were placed on the bottom of a 500 mL Erlenmeyer flask at the position labeled (1) in Figure 5. A flow of dry air (1-16 mL/s) at temperatures of 0-38°C was used to transfer the solid explosives to the gas phase. The measurements as function of temperature were done in two forms, scanning the range of temperature and fixed temperature point measurements. Traces of explosives in gas phase were dragged from the surface by the air flow and transported to an IR gas cell for detection. Spectra were recorded using the instrument first at 4 cm-1 of resolution and 25 scans were used for the experiments. A total of 1089 spectra of air with 2,4-DNT, 1194 spectra of air with TATP and 2200 spectra of air were recorded to generate the models. On the OP EM-27 active mode experiments were carried out at lab temperature (25oC) at 30 scans and 4 cm-1 resolution. The spectral range used was from 700 to 1600 cm-1. Experiments using QCL LaserTune™ active mode experiments were carried out at lab temperature of 20 °C at 1 spectrum and 4 cm-1 resolution. The spectral range used was from 830 to 1430 cm-1. The presence of TATP in air was determined by GC-MS, and the concentration of 2,4-DNT in air for different flow conditions and temperatures were calculated by calibration curves from GC-µECD. Finally, explosive traces (PETN, TNT and RDX) were deposited on travel baggage of 1 in2 size of

The automation and computerization of laboratories have been carried out with various important consequences. One of them is the rapid acquisition of large amounts of data. However, it is well know that acquiring such large amount of data is far from to providing appropriate answers quicker. Obtaining vibrational spectroscopy multivariate data is not synonymous with possessing vibrational information. The later must be interpreted and placed in context to convert it into useful information for the user. Chemometrics is the field

A great deal of chemometrics tools have been developed and tested. The most used of these tools to identify, quantify and classify data sets are those that make use of principal

of chemistry that provides the user with the required tools to enable that capability.

the presence of explosive TATP, 2,4-DNT and 2,4,6-TNT in the gas phase.

and analyzed with the QCL spectrometer.

**3. Chemometrics to vibrational spectral analysis** 

**Figure 4.** Experiment setup for detection of chemical warfare simulant in commercial bottles.

**Figure 5.** Schematic diagram of experimental setup used in the IR detection. Traces of explosives in gas phase were dragged by air flow and transported to a gas cell for detection.

The IR equipment used for the experiments was a model IFS 66v/S interferometer (Bruker Optics, Billerica, MA). For the experiments described, the system was equipped with a DTGS detector and a potassium bromide (KBr) beamsplitter. A spectroscopic measurement averaged 20 scans at a resolution of 4 cm-1 using OPUS Version 4.2 software in the range of 7500 – 400 cm-1. Target chemicals were TATP, 2,4-DNT and 2,4,6-TNT. Second, an EM-27 Open Path FT-IR interferometer (Bruker Optics, Billerica, MA) was used to obtain the IR spectral information of gas phase TATP samples with a (TE) cooled MCT detector. Third: Quantum Cascade Laser (QCL) based dispersive IR spectrometer LaserTune™ (Block Engineering, Marlborough, MA) was used to obtain the IR spectral information of TATP samples. An Agilent 6890 gas chromatograph (GC) coupled to an Agilent 5893 mass selective detector (MSD) with a capillary column: HP-5 MS 5% phenyl methyl siloxane, Length: 30.0 m, 250.0 µm in diameter and 0.25 µm of film thickness was used for detecting the presence of explosive TATP, 2,4-DNT and 2,4,6-TNT in the gas phase.

166 Multivariate Analysis in Management, Engineering and the Sciences

UVB) with quantum efficiencies of 90% (200 cm-1) to 95% (3600 cm-1) served as light detector (Figure 4) and calibration was performed using cyclohexane. Detection was performed with a light source in order to be carried out in the high-background environment conditions. In this experiment, six different bottle materials: clear-glass, green-glass, brown-glass, clearplastic, white-plastic and green-plastic were used to measure the amount of simulant (triethyl phosphate) within the container. Mixtures ranged from 0% to 100% (v/v) of

simulant and water, simulant and commercial beverage product were analyzed.

**Figure 4.** Experiment setup for detection of chemical warfare simulant in commercial bottles.

**Figure 5.** Schematic diagram of experimental setup used in the IR detection. Traces of explosives in gas

phase were dragged by air flow and transported to a gas cell for detection.

Figure 5 shows a schematic diagram of the experimental setup used in the investigation. Samples of 100-300 µg/cm2 of explosives were placed on the bottom of a 500 mL Erlenmeyer flask at the position labeled (1) in Figure 5. A flow of dry air (1-16 mL/s) at temperatures of 0-38°C was used to transfer the solid explosives to the gas phase. The measurements as function of temperature were done in two forms, scanning the range of temperature and fixed temperature point measurements. Traces of explosives in gas phase were dragged from the surface by the air flow and transported to an IR gas cell for detection. Spectra were recorded using the instrument first at 4 cm-1 of resolution and 25 scans were used for the experiments. A total of 1089 spectra of air with 2,4-DNT, 1194 spectra of air with TATP and 2200 spectra of air were recorded to generate the models. On the OP EM-27 active mode experiments were carried out at lab temperature (25oC) at 30 scans and 4 cm-1 resolution. The spectral range used was from 700 to 1600 cm-1. Experiments using QCL LaserTune™ active mode experiments were carried out at lab temperature of 20 °C at 1 spectrum and 4 cm-1 resolution. The spectral range used was from 830 to 1430 cm-1. The presence of TATP in air was determined by GC-MS, and the concentration of 2,4-DNT in air for different flow conditions and temperatures were calculated by calibration curves from GC-µECD. Finally, explosive traces (PETN, TNT and RDX) were deposited on travel baggage of 1 in2 size of and analyzed with the QCL spectrometer.
