Detection of Explosives and Related Compounds by Low-Temperature Plasma Ambient Ionization Mass Spectrometry

Abstract

Detection of explosives is important for public safety. A recently developed low-temperature plasma (LTP) probe for desorption and ionization of samples in the ambient environment ( Anal. Chem. 2008 , 80 , 9097 ) is applied in a comprehensive evaluation of analytical performance for rapid detection of 13 explosives and explosives-related compounds. The selected chemicals [pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), cyclo-1,3,5-trimethylenetrinitramine (RDX), tetryl, cyclo-1,3,5,7-tetramethylenetetranitrate (HMX), hexamethylene triperoxide diamine (HMTD), 2,4-dinitrotoluene, 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,6-dinitrotoluene, and 4-nitrotoluene) were tested at levels in the range 1 pg-10 ng. Most showed remarkable sensitivity in the negative-ion mode, yielding limits of detection in the low picogram range, particularly when analyzed from a glass substrate heated to 120 °C. Ions typically formed from these molecules (M) by LTP include [M + NO(2)](-), [M](-), and [M - NO(2)](-). The LTP-mass spectrometry methodology displayed a linear signal response over three orders of magnitude of analyte amount for the studied explosives. In addition, the effects of synthetic matrices and different types of surfaces were evaluated. The data obtained demonstrate that LTP-MS allows detection of ultratrace amounts of explosives and confirmation of their identity. Tandem mass spectrometry (MS/MS) was used to confirm the presence of selected explosives at low levels; for example, TNT was confirmed at absolute levels as low as 0.6 pg. Linearity and intra- and interday precision were also evaluated, yielding results that demonstrate the potential usefulness and ruggedness of LTP-MS for the detection of explosives of different classes. The use of ion/molecule reactions to form adducts with particular explosives such as RDX and HMX was shown to enhance the selectivity and specificity. This was accomplished by merging the discharge gas with an appropriate reagent headspace vapor (e.g., from a 0.2% trifluoracetic acid solution).

Non-contact halogen lamp heating assisted LTP ionization miniature rectilinear ion trap: a platform for rapid, on-site explosives analysis

“…As shown in Fig. 2 34 Unlike TNT and PETN, no signals are observed for RDX and tetryl at room temperature. This could be attributed to their low vapor pressures, as well as to the low discharge power of the LTP probe (only 0.27 W in our experiments) which was not high enough to assist the (thermal) desorption of the samples.…”

“…7, TNT and dinitrotoluene (DNT) can be found in this wastewater. According to the study by Cooks and co-workers, 34 the ion at m/z of 182 is assigned to 2,6-DNT, while ions at the m/z values of 181 and 183 are assigned to 2,4-DNT. The quantitative analysis of TNT in the wastewater was performed using an external standard calibration curve ranging from 10 to 500 pg, and a concentration of 5 ng mL À1 was suggested.…”

Trace Level Detection of Explosives in Solution Using Leidenfrost Phenomenon Assisted Thermal Desorption Ambient Mass Spectrometry

“…Heat is a very common source for desorption and can increase the detection sensitivity of explosives with several orders of magnitude. 19) When heat is supplied to a solution containing a non-volatile compound, the solution evaporates fast, leaving the sample residue on sample holder. If the sample is thermally labile in nature, then heat-associated dissociation could occur.…”

“…18,19) In this case the excited helium (He * ) reacted with atmospheric gases and generated secondary ions that reacted with explosive molecules. The strong appearance of [ − indicates that ion-molecule clustering reactions take place in ambient atmosphere.…”

“…In 2005, Takats et al reported the detection of several explosives from ambient surfaces by using desorption electrospray ionization (DESI) mass spectrometry. 13) Since then several other ambient mass spectrometric techniques like thermal desorption ambient ion/molecule reactions, 14) direct analysis in real time (DART), 15) extractive electrospray ionization (EESI), 16) dielectric barrier discharge ionization (DBDI), 17) low-temperature plasma (LTP), 18,19) etc. have been developed for direct detection of explosives from various surfaces and mixtures.…”