Some insights into the gas chromatographic determination of reduced sulfur compounds (RSCs) in air.

The analytical properties of four reduced sulfur compounds (RSCs), including hydrogen sulfide (H2S), methyl mercaptan (CH3SH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), were investigated to improve the techniques for their measurements at sub-part-per-billion (sub-ppb) concentration levels. Forthis purpose, a gas chromatographic (GC) system with a pulsed-flame photometric detector (PFPD) was interfaced with a thermal desorption (TD) unit for the collection and analysis of RSCs in ambient air. The calibration results obtained by working standards of equimolar concentrations (prepared at five different concentrations of 5, 10, 20, 50, and 100 ppb) were evaluated to properly describe the detection characteristics of the GC/ PFPD setting and of different RSCs. It was observed that the absolute magnitude of calibration slopes changed among different S compounds in a consistent manner (e.g., enhanced sensitivity toward the compound of heavy molecular weight and/or high sulfur contents), while their full scales of linearity range varied in an opposite pattern. The absolute magnitude of the H2S calibration slope values was remarkably sensitive to the initial standard concentrations, while such effects were not so evident from other RSCs. The overall results of this study suggest that the GC detection of H2S by means of the bag sampling technique can suffer from the strongest variability due to the dynamic change of its calibration in accord with its initial concentration.