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

摘要

ABSTRACT: Detection of explosives is important for publicnsafety. A recently developed low-temperature plasma (LTP)nprobe for desorption and ionization of samples in the ambientnenvironment (Anal. Chem. 2008, 80, 9097) is applied in a com-nprehensive evaluation of analytical performance for rapid detec-ntion of 13 explosives and explosives-related compounds. Thenselected chemicals [pentaerythritol tetranitrate (PETN), trini-ntrotoluene (TNT), cyclo-1,3,5-trimethylenetrinitramine (RDX),ntetryl, cyclo-1,3,5,7-tetramethylenetetranitrate (HMX), hexa-nmethylene triperoxide diamine (HMTD), 2,4-dinitrotoluene, 1,n3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,6-dinitrotoluene, and 4-nitrotoluene)nwere tested at levels in the range 1 pg-10 ng. Most showed remarkable sensitivity in the negative-ion mode, yielding limits ofndetection in the low picogram range, particularly when analyzed from a glass substrate heated to 120 u0001C. Ions typically formed fromnthesemolecules (M) by LTP include [MþNO2]n-, [M]n-, and [M-NO2]n-. The LTP-mass spectrometrymethodology displayedna linear signal response over three orders of magnitude of analyte amount for the studied explosives. In addition, the effects ofnsynthetic matrices and different types of surfaces were evaluated. The data obtained demonstrate that LTP-MS allows detection ofnultratrace amounts of explosives and confirmation of their identity. Tandem mass spectrometry (MS/MS) was used to confirm thenpresence of selected explosives at low levels; for example, TNT was confirmed at absolute levels as low as 0.6 pg. Linearity and intra-nand interday precision were also evaluated, yielding results that demonstrate the potential usefulness and ruggedness of LTP-MS fornthe detection of explosives of different classes. The use of ion/molecule reactions to form adducts with particular explosives such asnRDX and HMX was shown to enhance the selectivity and specificity. This was accomplished by merging the discharge gas with annappropriate reagent headspace vapor (e.g., from a 0.2% trifluoracetic acid solution).