The detection of illicit explosives in a large room, container, or cargo hold is problematic due to the current limitations in sampling and detection of explosives and to the size and time constraints of the search. Solid Phase MicroExtraction (SPME) can be used to rapidly extract volatile and semi-volatile compounds from the headspace of an explosive and ion mobility spectrometry (IMS) is a rapid presumptive organic detection technique that has already found widespread use in the detection of hidden explosives. SPME has recently been coupled to IMS as a sample pre-concentration device in order to improve the detection of explosives concealed in open areas. Detection limits have been determined for the following taggants: 2-nitrotoluene (2-NT), 4-nitrotoluene (4-NT), 2,3-dimethyl-2,3-dinitro butane (DMNB) and the following volatile explosive compounds: 2,4-dinitrotoluene, (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), and 2,4,6-trinitrotoluene (2,4,6-TNT). Nitrocellulose (NC) is also capable of being detected by the SPME-IMS system on a reliable basis. Results from these experiments point towards the usefulness of this technique as a potential screening tool for explosive compounds. Mass transport experiments are being conducted to determine the compound concentration in a flow of air for detection to occur. Further work will also be conducted using explosive odor signature compounds as potential illicit explosive detection compounds.
A comprehensive study and comparison is underway using biological detectors and instrumental methods for the rapid detection of ignitable liquid residues (ILR) and high explosives. Headspace solid phase microextraction (SPME) has been demonstrated to be an effective sampling method helping to identify active odor signature chemicals used by detector dogs to locate forensic specimens as well as a rapid pre-concentration technique prior to instrumental detection. Common ignitable liquids and common military and industrial explosives have been studied including trinitrotoluene, tetryl, RDX, HMX, EGDN, PETN and nitroglycerine. This study focuses on identifying volatile odor signature chemicals present, which can be used to enhance the level and reliability of detection of ILR and explosives by canines and instrumental methods. While most instrumental methods currently in use focus on particles and on parent organic compounds, which are often involatile, characteristic volatile organics are generally also present and can be exploited to enhance detection particularly for well-concealed devices. Specific examples include the volatile odor chemicals 2-ethyl-1-hexanol and cyclohexanone, which are readily available in the headspace of the high explosive composition C-4; whereas, the active chemical cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) is not. The analysis and identification of these headspace 'fingerprint' organics is followed by double-blind dog trials of the individual components using certified teams in an attempt to isolate and understand the target compounds to which dogs are sensitive. Studies to compare commonly used training aids with the actual target explosive have also been undertaken to determine their suitability and effectiveness. The optimization of solid phase microextraction (SPME) combined with ion trap mobility spectrometry (ITMS) and gas chromatography/mass spectrometry/mass spectrometry (GC/MSn) is detailed including interface development and comparisons of limits of detection. These instrumental methods are being optimized in order to detect the same target odor chemicals used by detector dogs to reliably locate explosives and ignitable liquids.