A preconcentration method based on a new sorbent for the measurement of selected reduced sulfur compounds at ppb level in ambient air

Odour annoyance forms the main source of environmental stress in residents living nearby industrial or agricultural fields. However, despite a relative simplicity of odour measurement at the emission source, odour measurement in the field is a quite more complicated task. Because of their low odour threshold and offensive odour, this study focuses on 6 reduced sulfur compounds (RSCs): methylmercaptan (MM), ethylmercaptan (EM), dimethylsulfide (DMS), isopropylmercaptan (IPM), tertbutylmercatpan (TBM), diethylsulfide (DES). Because of their very low concentrations in ambient air (few ppb), a preconcentration step is usually required. The literature points Tenax TA® as the more suitable sorbent for sulfur compounds adsorption but shows also an important impact of humidity and storage parameters inducing an underestimation of sulfur ambient air concentrations. So only qualitative or semi-quantitative data results are obtained with Tenax TA® samplings of targeted compounds. To guarantee quantitative concentration data, a new sampling device, using a S-Sorbent Tube450 combined with an optimal drying device, was performed and optimized sampling and analysis parameters were determined. The assessment of uncertainties attests of quantitative measurements for 5 of the 6 RSCs (EM, DMS, IPM, TBM, DES) with relative expanded uncertainties less than 33% considering that samples were stored properly in freeze during 7 days. Only semi-quantitative measurements could be considered for MM with a global uncertainty estimated to 48%, storage contributing for a half.