A study of sorptive loss patterns for reduced sulfur compounds in the use of the bag sampling method

In this work, the basic properties of the bag sampling method were examined and characterized in terms of recovery rate with respect to four reduced sulfur compounds (RSC) including H2S, CH3SH, DMS, and DMDS. For this comparative study, two types of calibration approaches were performed to evaluate the relative RSC loss due to bag sampling. As a reference calibration tool, a syringe dilution (SD) method was applied. The working standards prepared by diluting the primary standard in a gas-tight syringe (as a mixing chamber) were injected to the GC/PFPD through a loop-injection system to yield a background calibration information. In contrast, the target calibration was performed based on a bag dilution (BD) method. To this end, working standards for multiple calibration points were prepared by two different bag types (Tedlar bag (TB) and polyester bag (PB)). These standards were then drawn by the same syringe and injected into the GC/PFPD via loop. On the basis of these comparative analyses, both absolute and relative differences in RSC recovery rates (RR) were evaluated (e.g., comparison of wall-loss effect). The results indicate that TB has a mean RR of 87% for the four RSC with their values ranging from 82 (CH3SH) to 91% (DMDS). On the other hand, the results of PB generally exhibited slightly reduced RR with their mean values of 77% (range: 73% of H2S to 83% of DMS). The results of this study generally suggest that the losses of RSC samples, while inevitable with the bag sampling method, exhibit certain patterns between different RSCs and between different grab sampling materials.