Using Gas Chromatography with Ion Mobility Spectrometry to Resolve Explosive Compounds in the Presence of Interferents*

Abstract

Ion mobility spectrometry (IMS) is a valued field detection technology because of its speed and high sensitivity, but IMS cannot easily resolve analytes of interest within mixtures. Coupling gas chromatography (GC) to IMS adds a separation capability to resolve complex matrices. A GC-IONSCAN® operated in IMS and GC⁄ IMS modes was evaluated with combinations of five explosives and four interferents. In 100 explosive/interferent combinations, IMS yielded 21 false positives while GC⁄ IMS substantially reduced the occurrence of false positives to one. In addition, the results indicate that through redesign or modification of the preconcentrator there would be significant advantages to using GC⁄ IMS, such as enhancement of the linear dynamic range (LDR) in some situations. By balancing sensitivity with LDR, GC⁄ IMS could prove to be a very advantageous tool when addressing real world complex mixture situations.

Recent trends in organic gunshot residue analysis

“…Alternatively, IMS has been combined with GC to provide the separation of complex mixtures [59]. Although this inhibits field analysis, a reduction in false positives was demonstrated in a study by Cook et al [59].…”

“…A possible solution to this issue could be the use of a differential mobility analysis (DMA), which is a specific configuration of an IMS which facilitates the improvement in resolving powder and sensitivity, although it was not tested specifically for OGSR compounds [66]. Alternatively, IMS has been combined with GC to provide the separation of complex mixtures [59]. Although this inhibits field analysis, a reduction in false positives was demonstrated in a study by Cook et al [59].…”

“…GC-MS has frequently been used in recent OGSR analyses and the majority of the detected organic compounds associated with OGSR has been detected from propellant powder and spent cases using this technique [8,9,13]. GC can also be coupled to IMS to enable the separation of complex mixtures [59]. Detection limits of several nanograms per compound have been reported for GC-MS [2].…”

“…The advantages specific to IMS, especially the field-portability and near instantaneous analysis speeds, make IMS particularly suitable as a rapid, on site screening technique. Two anticipated difficulties of this technique are: the potentially insufficient separation power for complex mixtures, or when a greater amount of OGSR compounds is to be included in the analysis; and the lesser suitability as a confirmatory technique [59]. In a recent study by Arndt et al [67], however, IMS was used for the analysis of OGSR, which was collected from the shooter's hands using a swab.…”

Analysis of Botulinum Neurotoxin Detection by Mass Spectrometry in Forensic Samples

“…Examples of trace evidence are, not limited to, examinations of glass, fiber, paint, debris, gunshot residue (GSR), building material, inks, toners, fingerprint residue and among others [13][14][15][16][17]. A variety of analytical techniques, including use of UVvisible microspectrophotometry [18], Fourier transform infrared spectroscopy (FTIR) with total attenuated reflectance (ATR) [19], Surface-enhanced Raman spectroscopy (SERS) [20], scanning electron microscopy with energy dispersed X-ray spectrometry (SEM-EDS) [21], inductively coupled plasma optical emission spectrometry (ICP-OES) [22], atomic absorption spectroscopy (AAS) [23], scanning electrochemical microscopy (SECM) [24], atomic force microscopy (AFM) [25], confocal laser scanning microscopy (CLSM) [26], gas chromatography with mass spectrometry (GCMS) [27] capillary electrophoresis [28] (CE) , and laser inducedbreakdown spectroscopy (LIBS) [29], have been used to provide fundamental knowledge and insightful information for forensic cases. Photoacoustic spectroscopy is also used for quantitative and qualitative analysis of explosives, ink, paints, pigments and tissues [30][31][32][33][34][35][36].…”