Optimization of parameters of sampling and determination of reduced sulfur compounds using cryogenic capture and gas chromatography in tropical urban atmosphere

Abstract

Reduced sulfur compounds, RSCs (H2S, COS, CH3SH, CH3SCH3, CS2 and CH3S2CH3) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection. Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min− 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H2S, CH3SH and CH3S2CH3 the method showed a precision of 89%, limit of detection of 0.10 µg m− 3 and limit of quantification 0.3 µg m− 3. For CH3SCH3 and CS2 the corresponding values were 89%, 0.15 µg m− 3 and 0.5 µg m− 3 and for COS were 75%, 0.18 µg m− 3 and 0.8 µg m− 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H2S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics.