Electrospray Stand-off Detection of Trace Species in Air of Currency

To detect and identify vapors of contraband currency, not to mention a selection mode for explosives, narcotics, chemical warfare agents, biological threats or other analyte species at trace levels in air, is an important problem with many ramifications. One widely used approach is based on transforming the molecules of those species into gas phase ions, which are then characterized by measurements of their mobility. Research is proposed on evaluating two novel and prospectively major improvements in this approach. One is to use a variation on Electrospray Ionization for the transformation of gaseous analyte molecules into ions. The other is to apply Pseudo Random Chopping techniques to ion mobility spectrometry. Preliminary experiments have shown that ESI can readily produce useful ion currents from species at sub parts per billion concentrations with very large SN ratios in open air, a requirement for sensitive standoff sniffing of contraband currency now performed using dogs. Moreover, ESI ionizes only polar molecules, ignoring all the nonpolar species that are a great majority of the molecules in air and other matrix gases. This selectivity eliminates most of the chemical noise that is a serious problem in IMS, where resolving power is limited.