A nanoparticle-coated chemiresistor array as a microscale gas chromatograph detector for explosive marker compounds: flow rate and temperature effects

Abstract

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).

A microfabricated optofluidic ring resonator for sensitive, high-speed detection of volatile organic compounds

“…The effects of temperature and flow rate on the factors presented above can also be significant. 21,28,39 The LOD we calculated for m-xylene with the μOFRR above is 1-3 orders of magnitude lower than those of chemiresistor or surface-acoustic-wave microsensors employing sorptive nanoparticle or polymer interface layers that have been used as portable GC or μGC detectors under similar operating conditions; 16,17,21,40,41 reported LODs were in the range of 0.5-14 ng for m-xylene, though for peaks that were wider than those measured here by virtue of having been injected from an adsorbent preconcentrator and/or separated on an upstream (μ)column. The Fabry-Perot (FP) sensors explored as (μ)GC detectors by Reddy, et al, [24][25][26] were not tested with m-xylene, but an LOD of 200 pg for toluene was obtained by probing a PDMS film under conditions that gave a relatively broad toluene peak (i.e., FWHM ≈1 s).…”

Thermal aspects of a micro thermal conductivity detector for micro gas chromatography

“…In the present paper, we report on the fabrication, experimental characterization and modeling of a micro thermal conductivity detector (µTCD) to be used as part of a micro gas chromatography (µGC) device for IAQ monitoring in general, and Volatile Organic Compounds (VOCs) detection in particular [6]- [10].…”

Compact prototype microfabricated gas chromatographic analyzer for autonomous determinations of VOC mixtures at typical workplace concentrations

“…Members of our group have reported on a number of μGC and μGC × μGC components and systems in recent years [37][38][39][40][41][42][43][44][45][46][47][48][49][50] . We have also developed automated prototype instruments containing μGC systems for measuring low-to sub-ppb concentrations of trichloroethylene (TCE) in vapor-intrusion impacted homes 51,52 , and markers of explosives for transportation security 53,54 . Features common to these prototype instruments include a partially selective high-volume sampler of conventional design, a micromachined preconcentrator-focuser (μPCF) for focusing and injection, one or more μcolumns for temperature-programmed separations, and arrays of μchemiresistors (μCR) with thiolatemonolayer protected gold nanoparticle (MPN) interface films for multichannel detection and recognition of eluting VOCs.…”