Microfabricated Gas Chromatograph for On-Site Determination of Trichloroethylene in Indoor Air Arising from Vapor Intrusion. 1. Field Evaluation

Abstract

Results are presented of inaugural field tests of two identical prototype microfabricated gas chromatographs (μGC) adapted for the in situ determination of trichloroethylene (TCE) in indoor air in support of vapor intrusion (VI) investigations. Each μGC prototype has a pretrap and 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 multichannel detection. Scrubbed ambient air is used as the carrier gas. Field-generated calibration curves were linear for injected TCE masses of 26-414 ng (4.8-77 ppb·L; r(2) > 0.98) and the projected single-sensor detection limit was 0.052 ppb for an 8-L air sample collected and analyzed in 20 min. Consistent performance between the prototypes and good medium-term stability were shown. Above the mitigation action level (MAL) of 2.3 ppb for the field-test site, μGC TCE determinations fell within ±25% of those from the reference method for 21 of 26 measurements, in the presence of up to 37 documented background VOCs. Below the MAL, positive biases were consistently observed, which are attributable to background VOCs that were unresolvable chromatographically or by analysis of the sensor-array response patterns. Results demonstrate that this type of μGC instrument could serve the need for routine TCE determinations in VI-related assessment and mitigation efforts.