Fast gas chromatography negative chemical ionization tandem mass spectrometry of explosive compounds using dynamic collision-induced dissociation

The analysis of nine explosive compounds by gas chromatography tandem mass spectrometry (GC-MS/MS) using negative chemical ionization (NCI) was performed under two different conditions: first, a conventional GC separation coupled with a standard ion dissociation method in a quadrupole ion trap (QIT) was performed in segmented selected reaction monitoring mode; second, a fast GC separation on a microbore capillary column was combined with a faster method of collisional activation in ion traps wherein fragmentation is deliberately accomplished during the mass acquisition scan. The conventional GC-MS/MS method provided separation times in 10 min with detection limits between 0.8 and 280 pg on column. The fast GC method with dynamic collision-induced dissociation (DCID) offered a confirmatory method for the analysis of high explosives with separation times under 2.5 min and detection limits between 0.5 and 5 pg on column, without any hardware modifications to the instrument. The implementation of DCID in combination with three-times-faster mass scanning allows the acquisition of tandem mass spectra to at least 5 Hz (while averaging three scans per spectrum). Although detection limits for GC-NCI-MS/MS using conventional CID or DCID are not quite on par with LODs achieved by GC-ECD, the combination of NCI with DCID tandem MS leads to detection limits at least comparable, if not superior, to other mass spectrometric methods. Selected reaction monitoring in the negative ionization mode is anticipated to offer the most selective approach to detecting explosives and eliminating potential interferences, which could ultimately lead to the best detection limits for real, contaminated samples.