Improved selectivity for the determination of trinitrotoluene through reactive stage tandem ion mobility spectrometry...

A tandem ion mobility spectrometer was used to mobility isolate ions at the drift time for trinitrotoluene (TNT) in a first mobility stage, remove an interfering compound by ion decomposition in a middle reactive stage, and mobility characterize the remaining TNT ions in a second mobility stage. This sequential processing of ions provided decisive detection of TNT in the presence of an interfering peak differing from TNT in reduced mobility coefficient (K_o) by only 0.02 cm²/V. Even though ions of TNT (as M - 1)^- and the interfering compound were more than 90% convolved, TNT could be selectively detected with more than 95% decomposition of the interferent at 123 Td to an ion now separated by ΔK_o of 0.2 cm²/V from TNT. Ions for TNT were not decomposed in these electric fields though transmission efficiency was decreased by 20% through a wire grid assembly (the reactive stage). Although tandem ion mobility spectrometry with a reactive stage improves selectivity of measurement in the drift time dimension, the chemistry of ion formation in the ion source is affected still by ion suppression. Response to 1 ng TNT was decreased as much as 30% from 200 ng of interferent deposited on sample trap.