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

An automated gas chromatography system for analyzing atmospheric halocarbon s was constructed and evaluated. A cryogenic trap was developed to facilita te automation and, at the same time, conserve liquid nitrogen. Concentratio n calibration was accomplished by the use of multi-component gas mixtures w ith ambient concentration levels. Reproducibility was evaluated with replic ate precision of about 1-2% for most of the measured halocarbons, substanti ally 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, an d 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 uni form 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.