Environmental Sensors and Subsystems

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A Microscale Gas Chromatograph for High-Speed Determinations of Explosive Marker Compounds
Gustavo Serrano, Lindsay Amos, Hungwei Chang, Will Collin, Nicolas Nuñovero, and Edward T. Zellers

This project demonstrates the first fully integrated, fieldable, gas chromatographic microanalytical system (µGC) for near-real-time determinations of trace-level vapor concentrations of marker compounds of explosives. This µGC, dubbed INTREPID, will be used for airport screening applications to protect workers and the public from terrorist threats. A top view of the current field prototype is shown above. It uses an adsorbent-packed, deep-reactive-ion-etched (DRIE) Si/glass microfocuser, a wall-coated DRIE-Si/glass microcolumn, and an integrated array of 4 chemiresistors coated with functionalized thiolate-monolayer-protected gold nanoparticle (MPN) interface layers. The four MPNs are: n-octanethiol (C8), 6-phenoxyhexane-1-thiol (OPH), 4-(phenylethynyl)-benzenethiol (DPA), methyl-6-mercaptohexanoate (HME), each of which yields a unique response to eluting vapors. A high-volume sampler is connected upstream to reduce analysis time and detection limits. Commercial valves and mini-pumps are used. All functions are set and automatically sequenced by a laptop computer, which runs routines written in-house in LabView. Laboratory testing of the INTREPID field prototype was performed with the following explosive markers: 2,4- dinitrotoluene (2,4- DNT) and 2,3-dimethyl-2,3-dinitrobutane (DMNB, an explosive taggant). Calculated limits of detection are 2.2 and 0.85 ng, corresponding to 0.31 and 0.11 ppb, for DMNB and 2,4-DNT, respectively (1-L sample). In the analysis of the mixture of the two markers and 19 other compounds, all targets were completely resolved from the interferences and a complete analysis required just 2 min as shown by the chromatogram above. This work is funded by the U. S. Department of Homeland Security, Science and Technology Directorate.

Updated 03/31/2012