One- and Two-Dimensional Michaposcale Gas Chromatography Systems: Materials, Design and Implementation.

Abstract

This dissertation describes the development of prototype instrumentation containing gas chromatographic microanalytical systems (microGC) made from Si-microfabricated components for determining the components of complex mixtures of volatile/semi-volatile organic compounds (S/VOC). The core components are an adsorbent-packed micropreconcentrator-focuser (microPCF), a single- or dual-microcolumn separation module, and a detector comprising a single, polymer-coated microoptofluidic ring resonator (microOFRR) microsensor or an array of chemiresistor (CR) microsensors coated with various monolayer-protected Au nanoparticles (MPN). The latter produces selective response patterns that can enhance the discrimination of S/VOCs. The first prototype developed contains a single-microcolumn microGC system designed for rapid determinations of two vapor-phase markers of the explosive trinitrotoluene: 2,3-dimethyl-dinitrobenzene and 2,4-dinitrotoluene. A selective, high-volume sampler and an array of MPN-coated CRs held at elevated temperature enabled measurements of these targets at sub-parts-per-billion air concentrations in a 2-min sampling/analytical cycle among 20 interfering S/VOCs. The second prototype developed contains a dual-microcolumn microsystem designed to perform comprehensive two-dimensional gas chromatographic separations (microGC x microGC), wherein compounds separated on a first-dimension (1D) microcolumn are passed through a microscale thermal modulator (microTM) and further separated on a second-dimension (2D) microcolumn. First, the microTM was fluidically integrated with 1D and 2D microcolumns and the separation of a 36-component VOC mixture was demonstrated using a conventional detector. Next, this microGC x microGC separation module was integrated with the microOFRR detector, and the influence of analyte volatility on the response characteristics was illustrated. Detection limits (LOD) in the low-ng range and modulated peak widths in the 100-700 ms range were achieved for a set of common environmental contaminants. The next study demonstrated the advantages of programming the minimum and maximum microTM temperatures over the course of a microGC x microGC separation to enhance analyte resolution and detectability. Then, a CR array was installed as the detector and the effects of flow rate, temperature, and analyte volatility on resolution, sensitivity, and LOD were characterized. The final study entailed the integration of a dual-adsorbent microPCF to complete the assembly of the microGC x microGC prototype and initial measurements obtained therefrom.