Multi-stage preconcentrator/focuser module designed to enable trace level determinations of trichloroethylene in indoor air with a microfabricated gas chromatograph

Abstract

This article describes the development and characterization of a multi-stage preconcentrator/focuser (PCF) module designed to be integrated with a microfabricated gas chromatograph (µGC) for autonomous, in situ determinations of volatile organic compounds. The PCF module has been optimized specifically for the determination of trichloroethylene (TCE) vapors at low- or sub-parts-per-billion concentrations in the presence of common indoor air co-contaminants in residences at risk of vapor intrusion (VI) from surrounding TCE-contaminated soil. It consists of three adsorbent-packed devices arranged in series: a pre-trap of conventional (tubular metal) design for capturing interferences with vapor pressures <3 torr; a high-volume sampler, also of conventional design, for capturing (and transferring) TCE and other compounds with vapor pressures within the range of ~3 to 95 torr; and a microfocuser (µF) consisting of a micromachined Si chamber with an integrated microheater for focusing and injecting samples into the separation module. The adsorbent masses, sampling and desorption flow rates, and heating profiles required for selective, quantitative capture and transfer/injection of TCE are determined for each of the devices, and the assembled PCF module is used to analyze a test atmosphere containing 200 parts-per-trillion of TCE and 27 relevant co-contaminants with a conventional downstream capillary column and electron-capture detector. An average TCE transfer efficiency of 107% is achieved for a 20 L air sample, with a preconcentration factor of ~800,000.