A methodology for processing spectroscopic information using a chemometrics-based analysis was designed and implemented in the detection of highly energetic materials (HEMs) in the gas phase at trace levels. The presence of the nitroaromatic HEM 2,4-dinitrotoluene (2,4-DNT) and the cyclic organic peroxide triacetone triperoxide (TATP) in air was detected by chemometrics-enhanced vibrational spectroscopy. Several infrared experimental setups were tested using traditional heated sources (globar), modulated and nonmodulated FT-IR, and quantum cascade laser- (QCL-) based dispersive IR spectroscopy. The data obtained from the gas phase absorption experiments in the midinfrared (MIR) region were used for building the chemometrics models. Partial least-squares discriminant analysis (PLS-DA) was used to generate pattern recognition schemes for trace amounts of explosives in air. The QCL-based methodology exhibited a better capacity of discrimination for the detected presence of HEM in air compared to other methodologies. 1. Introduction The detection of highly energetic materials (HEMs) at trace levels in air remains a subject of great importance to national defense and security. In the past few years, most of the published reports have focused on the detection of these important chemical compounds. However, the majority of them require some type of sampling [1, 2]. Obtaining samples in the field is the principal disadvantage of most explosive detection devices because the person doing the sampling is at risk. Most of the analytical techniques employed for the development of methodologies for HEM detection are based on spectroscopic and chromatographic techniques [1, 2]. Trace amounts of 2,4-dinitrotoluene (2,4-DNT) in air have been detected and discriminated by surface-enhanced Raman spectroscopy (SERS) using a gold surface sensor [3]. These sensors generate a response in the presence or absence of 2,4-DNT and other volatile nitroaromatic HEMs in air. In this case, the sample vapor was introduced to the sensor with a fan. High-speed fluorescence spectroscopy is another method for the detection of nitroaromatic HEM in the air. This method employs silica microspheres coated with a highly sensitive fluorescent polymer that responds by quenching the fluorescence when HEM molecules attach to the polymer [1, 2, 4–7]. 2,4-DNT can also be detected and quantified by measuring the IR acoustic wave in polymer-coated surfaces [8]. In this method, the presence of 2,4-DNT generates a change in the frequency of the acoustic wave on the surface, and this change is used for
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