Identification of volatile chemical signatures from plastic explosives by SPME-GC/MS and detection by ion mobility spectrometry

Abstract

This study demonstrates the use of solid-phase microextraction (SPME) to extract and pre-concentrate volatile signatures from static air above plastic explosive samples followed by detection using ion mobility spectrometry (IMS) optimized to detect the volatile, non-energetic components rather than the energetic materials. Currently, sample collection for detection by commercial IMS analyzers is conducted through swiping of suspected surfaces for explosive particles and vapor sampling. The first method is not suitable for sampling inside large volume areas, and the latter method is not effective because the low vapor pressure of some explosives such as RDX and PETN make them not readily available in the air for headspace sampling under ambient conditions. For the first time, headspace sampling and detection of Detasheet, Semtex H, and C-4 is reported using SPME-IMS operating under one universal setting with limits of detection ranging from 1.5 to 2.5 ng for the target volatile signatures. The target signature compounds n-butyl acetate and the taggant DMNB are associated with untagged and tagged Detasheet explosives, respectively. Cyclohexanone and DMNB are associated with tagged C-4 explosives. DMNB is associated with tagged Semtex H explosives. Within 10 to 60 s of sampling, the headspace inside a glass vial containing 1 g of explosive, more than 20 ng of the target signatures can be extracted by the SPME fiber followed by IMS detection.

Fast Chromatographic Method for Explosive Profiling

“…An integral part of these security processes is to detect explosive devices. Different tools are used to achieve this task including detection dogs [1], ion mobility spectrometry (IMS) [2][3][4], gas chromatography (GC) [5], and liquid chromatography (LC) [6]. Nevertheless, one of the most accurate and sensitive means of screening for explosives remains the use of explosive detection dogs [1].…”

“…To improve the training process, investigators need to know the exact composition of the explosives, and more specifically, the gas phase composition of these samples (i.e., the volatile signature). Unfortunately, the main components of the explosives compounds are not thermally stable and have considerably low vapor pressures, presenting major challenges for obtaining an accurate representation of the volatile signatures [2,7]. Moreover, the analysis of the volatile signature of explosives is usually complicated due to the potential contamination contributed from storage conditions.…”

“…Several techniques have been developed previously that allow generation of vapor from explosives samples to provide a sufficient quantity of volatiles for analysis [8][9][10][11]. Solid phase micro-extraction (SPME) provides sufficient pre-concentration for most explosives samples and is therefore used widely [1,2,5,12,13]. Moreover, SPME is also used for volatile sample analysis in other forensic applications, such as chemical warfare agent detection [14], illicit drug detection [1], and decomposition odor monitoring [15].…”

“…Thus, IMS cannot provide the full volatile organic compounds (VOC) profile from one sample, which limits the ability to exploit the entire volatile signature for sample-to-source identification. For this reason, gas chromatography-mass spectrometry (GC-MS) methods are also used to provide a non-targeted approach that can generate a global characterization of the entire volatile signature [2,5]. Due to the low volatility of explosives, the minor components (e.g., components other than the active agents) are often targeted in research and focus on degradation products or source contamination [1,7].…”

Evaluation of Non-Contact Sampling and Detection of Explosives using Receiver Operating Characteristic Curves

“…Canine detection dogs have been shown to target volatile organic compounds that are associated with the given compound and training kits have been designed to contain the chemical compound rather than the illicit substance itself. Similarly, trace detection systems can be programmed to detect the volatile chemicals associated with the illicit compounds rather than the parent compound [33,34].…”