The loss patterns of reduced sulfur compounds in contact with different tubing materials

To collect or transfer samples of airborne pollutants, tubings made of various materials are used. To analyze the reactive loss patterns of reduced sulfur compounds (RSC) in the use of tubing fittings, a series of laboratory experiments were conducted so that the concentration changes were induced by the physical contact between gas samples and tubing walls. For the purpose of this study, a total of five tubing materials were investigated in reference to silcosteel (S1) tubing: stainless steel (S2), silicone (S3), PTFE Teflon (T1), tygon (T2), and copper (C). This comparative experiment was made using gaseous standards containing equimolar concentrations of four RSCs (H2S, CH3SH, DMS, and DMDS). The loss patterns of RSC were then evaluated and compared in terms of their calibration slope values across different tubing materials. The results of this comparative analysis indicated that except for a few cases, a fairly good compatibility was seen consistently among different tubing types and different RSCs. The results generally showed that the magnitude of calibration slope values obtained from different tubing materials tend to increase with an increase in RSC molecular weights. If the results are compared between different tubing materials, a highly contrasting pattern was evident. For instance, C tubing shows significant losses of light RSCs (H2S and CH3SH), while S3 tubing experiences the large losses of DMS and DMDS. A line of evidence found in this study thus suggests that most tubing types have their unique loss mechanism for RSCs, when they contact RSCs in sample gas stream passing through the tubing walls.