A nanoparticle-coated chemiresistor array as a microscale gas chromatograph detector for explosive marker compounds: flow rate and temperature effects†
The effects of flow rate and temperature on the performance of a microscale gas chromatographic (μGC) detector consisting of a chemiresistor (CR) array coated with different thiolate-monolayer-protected gold nanoparticles (MPNs) are described with respect to the analysis of three gas-phase markers of the explosive trinitrotoluene (TNT): 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), and 2,3-dimethyl-2,3-dinitrobutane (DMNB). In chamber tests, sensors were stable at 70 °C for several days in air, with <2% sensitivity drift per day and virtually no change in the array response patterns. In tests with a conventional upstream GC column, increasing the array temperature from 55–80 °C (1.2 mL min−1) led to similar (i.e., 4–6.6-fold) decreases in sensitivity, increases in the limits of detection (LODs), and increases in (estimated) chromatographic resolution. Increasing the flow rate from 1.1–3.7 mL min−1 (70 °C) led to ∼1.3–2-fold decreases in sensitivity and LOD for 2,4-DNT and 2,6-DNT, a ∼2-fold net increase in LOD for DMNB (passes through a maximum), and a <2-fold increase in resolution. Results indicate that the rates of desorption of the marker vapors out of the MPN films are important determinants of observed trends. With Si-micromachined focuser/injector and separation column devices placed upstream of a CR array held at 70 °C, a mixture of the two primary markers, 2,4-DNT and DMNB, and four similarly volatile alkane interferents was separated in 1.5 min at 3 mL min−1.