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

摘要

This article describes the development and characterization of a multi-stage preconcentrator/focusern(PCF) module designed to be integrated with a microfabricated gas chromatograph (mGC) fornautonomous, in situ determinations of volatile organic compounds. The PCF module has beennoptimized specifically for the determination of trichloroethylene (TCE) vapors at low- or sub-parts-perbillionnconcentrations in the presence of common indoor air co-contaminants in residences at risk ofnvapor intrusion (VI) from surrounding TCE-contaminated soil. It consists of three adsorbent-packedndevices arranged in series: a pre-trap of conventional (tubular metal) design for capturing interferencesnwith vapor pressures <3 torr; a high-volume sampler, also of conventional design, for capturing (andntransferring) TCE and other compounds with vapor pressures within the range of u00023 to 95 torr; andna microfocuser (mF) consisting of a micromachined Si chamber with an integrated microheater fornfocusing and injecting samples into the separation module. The adsorbent masses, sampling andndesorption flow rates, and heating profiles required for selective, quantitative capture and transferinjection of TCE are determined for each of the devices, and the assembled PCF module is used tonanalyze a test atmosphere containing 200 parts-per-trillion of TCE and 27 relevant co-contaminantsnwith a conventional downstream capillary column and electron-capture detector. An average TCEntransfer efficiency of 107% is achieved for a 20 L air sample, with a preconcentration factornof u0002800 000.