Characterization of a high-performance portable GC with a chemiresistor array detector

Abstract

The laboratory characterization of a novel, second-generation portable gas chromatograph (GC) prototype designed for trace-level determinations of complex mixtures of volatile organic compounds (VOC) is described. The instrument incorporates a small, multi-stage adsorbent preconcentrator/injector (PCI), two series-coupled separation columns with fast, independent temperature-programming capabilities and junction-point pressure/flow control, and a detector consisting of an array of microfabricated chemiresistor (CR) sensors coated with thiolate-monolayer-protected gold nanoparticle films. Response patterns from the CR array are used in conjunction with chromatographic retention times to identify eluting mixture components. Scrubbed ambient air is used as the carrier gas. Enhancements in design relative to a previously reported first-generation prototype instrument have led to significant reductions in limits of detection as well as improvements in resolution, reliability, flexibility, and convenience. Key features of the instrument are characterized, with an emphasis on the tradeoffs in sensor array performance associated with operation at different temperatures and flow rates. The separation of a preconcentrated mixture of 31 VOCs in < 7 minutes is demonstrated. Projected detection limits are in the ppt range for most compounds, assuming a 1 L sample volume.