Validation of a laboratory-constructed automated gas chromatograph for the measurement of ozone precursors through comparison with a commercial analogy

An automated gas chromatographic (auto-GC) system aiming at performing unattended hourly measurement of ozone precursors was developed in the laboratory. To encompass volatile organic compounds (VOCs) of a wide range of volatility within each analysis, the system uses dual-traps and dual-columns to simultaneously analyze both low and high-boiling compounds with each injection. Since sorbents with sufficient retention of C2 compounds at room temperature, namely ethane, ethene, and ethyne are not yet available, cooling with a thermoelectrical device was built around the low-boiling trap to facilitate quantitative enrichment of C2 compounds. The effectiveness of using micro-trap with low dead volume plumbing was manifested in reducing peak width and increasing peak height for particularly the lower-boiling compounds. The increase in sensitivity allowed sufficient detector response with a small amount of air sample, e.g. 200 ml in our routine operation, which in term eliminate the need for remove water prior to sampling trapping. The performance and applicability of this laboratory-built auto-GC system was validated by comparison with a commercial analog, i.e. the ATD-400 system made by Perkin-Elmer, in the field sharing a common air intake. During more than 3 weeks of synchronized monitoring of ambient volatile organic compounds both systems showed highly consistent results on almost every monitored compound, clearly demonstrating the robustness of this self-built system.