A Micro-Analytical System for Complex Vapor Mixtures - Development and Application to Indoor Air Contaminants.

Abstract

This dissertation concerns the development of two fully integrated, automatically controlled, field-deployable Si-microfabricated gas chromatograph (µGC) prototypes, and their application to indoor-air monitoring of trace-level trichloroethylene (TCE) vapor concentrations. Each µGC prototype has a pre-trap and a partially selective high-volume sampler of conventional design, a micromachined-Si focuser for injection, dual micromachined-Si columns for separation, and an integrated array of four microscale chemiresistors with functionalized gold-nanoparticle interface films for detection. Scrubbed ambient air is used as the carrier gas. Operating conditions and control settings are user-defined through a laptop computer, providing real-time data display and continuous unattended operation. A meso-scale GC employing the same detector technology as in the µGC prototypes was adapted for the same application, and the laboratory results obtained were used to guide the design and operating conditions of the µGCs. Application of a multivariate curve resolution method for deconvoluting microsensor array responses from partially overlapping interferences was also demonstrated. The µGC prototypes were characterized in the laboratory and then field tested in Utah in a house with active TCE vapor intrusion. In the laboratory, the separation of TCE from 45 other VOCs in < 60 sec, unique sensor-array response patterns, and accurate quantification of as little as 0.12 parts per billion (ppb) of TCE were demonstrated. In the field, the projected single-microsensor detection limit was 0.052 ppb for an 8-L air sample collected and analyzed in 20 min. Above the mitigation action level (MAL) of 2.3 ppb for the field-test site, accurate TCE determinations were achieved in the presence of up to 52 documented background VOCs. Below the MAL, positive biases were observed, which are attributable to background VOCs that were unresolvable chromatographically or by analysis of the sensor-array response patterns. Spatial and temporal variations in TCE concentrations, ranging from 0.23 to 56 ppb, provided by the prototypes were in good agreement with reference method values. This is the first study to validate the performance of a µGC in the field. Results demonstrate that µGC technology could provide selective, trace-level, on-site determinations of VOCs in numerous applications relevant to occupational and environmental exposure assessment.