Direct Analysis in Real Time Coupled to Multiplexed Drift Tube Ion Mobility Spectrometry for Detecting Toxic Chemicals

Authors: Glenn Harris, Facundo Fernndez, Mark Kwasnik
Anal Chem 2011, Mar, 15, 83(6), 1908-15


Current and future chemical threats to homeland security motivate the need for new chemical detection systems to provide border, transportation, and workplace security. We present the first successful coupling of a commercial direct analysis in real time (DART®) ion source to a resistive glass monolithic drift tube ion mobility spectrometer (DTIMS) as the basis for a low maintenance, versatile, and robust chemical monitoring system. in situ ionization within the electric field gradient of the instrument enhances sensitivity and provides a safe sampling strategy. The instrument uses nitrogen as both the DART® discharge and DTIMS drift gases, allowing for a high electric field to be used for ion separation while keeping cost-of-use low. With the use of a traditional signal averaging acquisition mode, the 95% probability of detection (POD) for analytes sampled from melting point capillary tubes was 11.81% v/v for DMMP, 1.13% v/v for 2-CEES, and 10.61 mM for methamidophos. Sensitivity was improved via a prototype transmission-mode geometry interface, resulting in an almost 2 orders of magnitude decrease in the POD level for DMMP (0.28% v/v). As an alternative to transmission mode operation, digital multiplexing of the DTIMS ion injection step was also implemented, finding a 3-fold improvement in signal-to-noise ratios for 200 ?s gate injections and a 4.5-fold for 400 ?s gate injections.
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