Temperature-dependent collection efficiency of a cryogenic trap for trace-level volatile organic compounds

Reduced temperature preconcentration of volatile organic compounds in a packed trap is examined experimentally as a function of trapping temperatures ranging from -180C to +100C. Trapped compounds are thermally desorbed into a capillary column-equipped gas chromatograph and quantified with a flame ionization detector. Data sets are presented for 21 compounds of environmental interest at various concentrations (in dry zero air) in the range of 0.1 ppbv to 100 ppbv. Measured chromatographic peak areas increase from a low but non-zero value for high trap-temperature runs to a constant value as the trap temperature is lowered. Extrapolated Clausius-Clapeyron equations are shown to be a useful guide in estimating the trap temperature required for 99% collection efficiency.