Gas chromatography positive chemical ionization and tandem mass spectrometry for the analysis of organic high explosives

The characteristic ions or the parent ion resulting from ionization can be isolated in an ion trap and subjected to further fragmentation during a gas chromatography–tandem mass spectrometry (GC/MS/MS) experiment. This approach can improve the selectivity and sensitivity of explosive compounds over gas chromatography–mass spectrometry (GC/MS) by improving the differentiation of the target compounds from interfering and co-eluting compounds and reducing the background noise within an explosive debris sample. The optimization of the operating parameters for GC/MS and GC/MS/MS experiments with an ion trap mass spectrometer were conducted using a mixture of explosive compounds and 3,4-dinitrotoluene as an internal standard. The level of detection (LOD) and limit of quantitation (LOQ) for these compounds was determined by GC/MS with electron ionization, GC/MS with positive chemical ionization, and GC/MS/MS with positive chemical ionization. The LOD range was found to be 3.6 pg for 2,4-dinitrotoluene to 2.23 ng for hexahydro-1,3,5-trinitro-s-triazine (RDX) using GC/EI/MS; 0.4 pg for 2,4-dinitroltoluene to 19.0 pg for 1,3,5-trinitrobenzene using GC/PCI/MS; and 0.5 pg for 4-nitrotoluene to 41.4 pg for RDX using GC/PCI/MS/MS. The LOD results for GC/PCI/MS and for GC/PCI/MS/MS are very similar for most of the compounds except the GC/PCI/MS LOD results are lower for RDX and 1,3-dinitrobenzene while the GC/PCI/MS/MS LOD results are lower for 1,3,5-trinitrobenzene. The GC/PCI/MS/MS method offers improved selectivity when analyzing real world samples containing interfering products and matrix noise thereby improving sensitivity for complex samples.