The performances of two nominally identical automated monitors for quantifying volatile organic compounds were compared on identical ambient laboratory air samples. The monitors incorporate cryogenic preconcentration subunits specially designed for controlled release of liquid nitrogen to establish a −150°C trap temperature. Measured trends in concentration for perchloroethylene, toluene, chloroform, Freon 113, methyl chloroform, and benzene showed good agreement even at sub-ppbv levels during automated overnight runs, although some effects of adsorption were evident. In a second set of runs, concentration results for one system were plotted versus those for the other. The plots were linear and, precise, but slightly biased. Qualitative comparisons using diluted automobile exhaust are also shown.
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McClenny et al. (1985) studied this question.