Cryogen free automated gas chromatography for the measurement of ambient volatile organic compounds

Abstract

An automated gas chromatographic system was constructed for measuring ambient volatile organic compounds (VOCs). Preconcentration of the VOCs was performed by using two separated sorbent traps of different combinations with each designated for either low or high boiling VOCs. Both traps and their associated valve systems were integrated as a complete system sharing a common sample inlet. Precise temperature controls for desorption relied on the use of a process controller with proportional-integral-derivative algorithm to throttle the current supply. No additional cryo-focusing stage prior to the column was needed owing to the flash heating capability for desorption. Other than the cryogen free preconcentration and focusing, the separation of VOCs of large volatility difference was also performed without cryogen. The system employed an Al 2O 3/KCl porous-layer open tubular column for separating C 3–C 7 compounds; and a DB-1 column for C 6–C 12. This automated GC system has been deployed in a Taiwan Environmental Protection Agency urban air quality monitoring station of Taiwan for continuous measuring C 3–C 7 ozone precursors. Excellent correlation between the car exhaust type of compounds measured by our GC system and carbon monoxide measured by a non-dispersive infrared spectrometer was observed, suggesting the automated GC system was robust and reliable.