Selective Reagent Ions for the Direct Vapor Detection of Organophosphorus Compounds Below Parts-per-Trillion Levels

Real-time low to sub parts-per-trillion (pptv) vapor detection of some organophosphorous compounds (OPCs) is demonstrated with an atmospheric flow tube–mass spectrometer. The chemical species investigated included dimethyl methylphosphonate, triethyl phosphate, and tributylphosphate. The atmospheric flow tube provides ambient chemical ionization with up to several seconds of ionization time. With sensitivities in the parts-per-quadrillion (ppqv) range, there are many background contaminants competing for charge with the target analytes. Initially, the OPCs were not observable in direct room air analysis, presumably due to other trace components possessing higher proton affinities. However, the addition of a trialkylamine as a dopant chemical served to provide a single reagent ion that also formed a proton-bound heterodimer with the OPCs. These asymmetric proton-bound dimers had sufficiently high hydrogen bond energy to allow the cluster to remain intact during the analysis time of several seconds. Changes...