STANDOFF INFRARED VIBRATIONAL DETECTION OF HIGHLY ENERGETIC MATERIALS ON NON-REFLECTIVE SUBSTRATES
The detection of threat chemicals in bulk and trace levels present in various matrices: gases/vapors, liquids, and solids is an important consideration for the development of sensors and standoff detection systems for use in National Defense and Security applications. Hazardous compounds such as highly energetic materials (HEM), homemade explosives (HME), chemical and biological agents are classified as imminent threats which provide terrorists to cause damage to civilians or troops. Our research on standoff detection systems allows detecting, discriminating and quantifying HEM on world-real substrates in a fast and reliable manner. Several infrared experimental setups were tested using traditional thermal sources (globar), modulated FT-IR, and quantum cascade laser (QCL) based on pre-dispersive IR spectroscopy. TLC-QCLS as a portable hyphenated technique for explosives analysis was also investigated. Substrates such as aluminum, travel bags, cardboard and wood were used. The HEM used were 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX). Hit quality index (HQI) values were calculated from a spectral library and used as a first identification method through correlation coefficients. Three chemometrics algorithms were applied to analyze the spectral characteristics. Partial least squares (PLS) regression was used to find the best correlation between the infrared signals and the surface concentrations of the samples. Principal component analysis (PCA) and PLS combined with discriminant analysis (PLS-DA) were used to discriminate, classify and identity similarities in the spectral data sets. The results demonstrate that the infrared vibrational method used in these studies can be useful for a rapid analysis of HEMs on real-world substrates.