Analysis of explosives using corona discharge ionization combined with ion mobility spectrometry–mass spectrometry

Corona discharge ionization combined with ion mobility spectrometry–mass spectrometry (IMS–MS) was utilized to investigate five common explosives: cyclonite (RDX), trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotetramethylenetetranitramine (HMX), and 2,4-dinitrotoluene (DNT). The MS scan and the selected ion IMS analyses confirmed the identities of the existing ion species and their drift times. The ions observed were RDX·NO3−, TNT−, PETN·NO3−, HMX·NO3−, and DNT−, with average drift times of 6.93 ms, 10.20 ms, 9.15 ms, 12.24 ms, 11.30 ms, and 8.89 ms, respectively. The reduced ion mobility values, determined from a standard curve calculated by linear regression of (normalized drift times)−1 versus literature K0 values, were 2.09, 1.38, 1.55, 1.15, 1.25, and 1.60 cm2 V−1 s−1, respectively. The detection limits were found to be 0.1 ng for RDX, 10 ng for TNT, 0.5 ng for PETN, 5.0 ng for HMX, and 10 ng for DNT. Simplified chromatograms were observed when nitrogen, as opposed to air, was used as the drift gas, but the detection limits were approximately 10 times worse (i.e., less sensitivity of detection).