Construction and evaluation of automated gas chromatography for the measurement of anthropogenic halocarbons in the atmosphere

An automated gas chromatography system for analyzing atmospheric halocarbons was constructed and evaluated. A cryogenic trap was developed to facilitate automation and, at the same time, conserve liquid nitrogen. Concentration calibration was accomplished by the use of multi-component gas mixtures with ambient concentration levels. Reproducibility was evaluated with replicate precision of about 1-2% for most of the measured halocarbons, substantially better than that of our previous manual system of 4-6%. The linearity of this automated system was confirmed by two independent methods, with one varying injection volume and the other varying injection concentration, and both were in excellent agreement. The system was successfully employed in canister and in-situ measurements. Concentrations of CCl4 was found to be extremely uniform with average concentration of 102 pp (v/v), very close to its global background value. The standard deviation of 106 samples was 1.5% for CCl4 which is almost equivalent to its analytical precision. This uniform property associated with CCl4 atmospheric distribution can be a useful tool for testing system's reproducibility and stability. (C) 1999 Elsevier Science B.V. All rights reserved.