A carefully designed study was conducted during the summer of
1998 to collect samples of ambient air by canisters and compare the analysis
results to direct sorbent preconcentration results taken at the time of sample
collection. Thirty-two 1 h sample sets were taken, each composed
of a “near-real-time” sample analyzed by an autoGC-MS XonTech
930/Varian Saturn 2000 system, and Summa and Silco canisters. Hourly total
non-methane organic carbon (TNMOC), ozone, and meteorological measurements
were also made. Each canister was analyzed on the autoGC-MS system for a target
list of 108 volatile organic compounds (VOCs) and on a manual cryosampling
GC-FID system. Comparisons were made between the collection and analysis methods.
Because of the low sample loading (150–250 ppbC TNMOC),
these comparisons were a stringent test of sample collection and analysis
capabilities. The following specific conclusions may be drawn from this study.
Reasonable precision (within 15% mean difference of duplicate
analyses from the same canister) can be obtained for analyses of target
VOCs at low-ppbC concentrations. Relative accuracy between the GC-MS and
GC-FID analysis methods is excellent, as demonstrated by comparisons of analyses
of the same canisters, if measurements are sufficiently above the detection
limits. This is especially significant as the GC-MS and GC-FID were independently
calibrated. While statistically significant differences may be observed between
the results from canister and near-real-time samples, the differences
were generally small and there were clear correlations between the canister
results and the near-real-time results. Canister cleanliness limits
detection below the EPA Method TO-14 acceptance standard of 0.2 ppbv (0.2–2 ppbC
for target analytes).
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