Fieldable MEMS gas chromatograph for rapid determinations of explosive marker compounds in complex mixtures

A field-ready prototype employing an all-MEMS gas chromatographic microsystem (μGC) for the determination of explosive marker compounds at low concentrations is described. The μGC prototype, which is referred to as INTREPID, relies on a core of Si-micromachined components. The microfabricated analytical subsystem consists of a DRIE-Si/glass microfocuser (μF) packed with a bed of graphitized carbon adsorbent material, a DRIE-Si/glass microcolumn (μcolumn) with integrated heater and temperature sensors wall-coated with PDMS, and a chemiresistor (CR) array consisting of 4 sets of interdigital gold electrodes coated with thiolate-monolayer protected nanoparticles (MPN). A high volume sampler is included upstream of the μF to reduce limits of detection and analysis time. The instrument is controlled by a laptop running routines written in LabView. The three target analytes are 2,4-dinitrotoluene (2,4-DNT), and 2,6-dinitrotoluene (2,6-DNT), which are manufacturing byproducts of 1,3,5-trinitrotoluene (TNT), as well as the taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB). A set of volatile organic compounds representative of jet fuel and common indoor air contaminants, was used to test the selectivity of the prototype. A complete analytical cycle requires 2 min and includes sampling, focusing, injection, separation, and detection. Limits of detection determined with the micro-analytical subsystem were 2.2, 0.5, and 0.9 ng for DMNB, 2,6-DNT, and 2,4-DNT which correspond to 0.30, 0.06, and 0.12 ppb in a 1-L air sample. CR-array response patterns are used to differentiate the markers from interferences.