A critical review of ion mobility spectrometry for the detection of explosives and explosive related compounds

Ion mobility spectrometry has become the most successful and widely used te chnology for the detection of trace levels of nitro-organic explosives on h andbags and carry on-luggage in airports throughout the US. The low detecti on limits are provided by the efficient ionization process, namely, atmosph eric pressure chemical ionization (APCI) reactions in negative polarity. An additional level of confidence in a measurement is imparted by characteriz ation of ions for mobilities in weak electric fields of a drift tube at amb ient pressure. Findings from over 30 years of investigations into IMS respo nse to these explosives have been collected and assessed to allow a compreh ensive view of the APCI reactions characteristic of nitro-organic explosive s. Also, the drift tube conditions needed to obtain particular mobility spe ctra have been summarized. During the past decade, improvements have occurr ed in IMS on the understanding of reagent gas chemistries, the influence of temperature on ion stability, and sampling methods. In addition, commercia l instruments have been refined to provide fast and reliable measurements f or on-site detection of explosives. The gas phase ion chemistry of most exp losives is mediated by the fragile C-ONO2 bonds or the acidity of protons. Thus, M- or M.Cl- species are found with only a few explosives and loss of NO2, NO3 and proton abstraction reactions are common and complicating pathw ays. However, once ions are formed, they appear to have stabilities on time scales equal to or longer than ion drift times from 5-20 ms. As such, peak shapes in IMS are suitable for high selectivity and sensitivity. (C) 2001 Elsevier Science B.V. All rights reserved.