dc.description.abstract | Reduced sulfur compounds (RSCs) are commonly found in ambient air, which easily give off foul odor in the environment at very low concentrations, thus affecting the quality of life for residents near the sources. In addition, RSCs also have significant implications in global climate change. The objective of this research is to develop a GC technique to analyze ambient H2S, C2H5SH, CH3SCH3, CS2, and CH3SSCH3 of RSCs using pulsed flame photometric detector (PFPD). Common challenges in the analysis of ambient RSCs include: 1. low concentration detection, 2. sample integrity due to high reactivity, 3. wall effect arising from the “stickiness” of RSCs on tubing or container’s inner surface, 4. the loss of H2S to water or oxidation, etc.
Ambient RSCs are often found at levels from ppbv to pptv, which is below the detection limits of a GC detector. As a result, a preconcentration step is needed prior to GC analysis to allow quantitative analysis. The performance of preconcentration relies largely on the proper selection of sorption materials. In this research, several materials tested at various trapping temperatures for the low levels of RSCs.
The Taiwan EPA method (NIEA A701.11C) uses Molecular Sieve 5A and Tenax TA to preconcentrate H2S and other sulfur compounds, respectively. This study is aimed at finding a single suitable sorption material which can enrich all RSCs within each sample aliquot with improved efficiency, manifested by better precision, linearity and lower limits of detection (LOD). The pore sizes of the test materials ranged from microporous (< 20Å) to macroporous ( >500Å ). Of the 17 materials tested, it was found that Unibeads 1S out-performed the rest in all criteria of quality assurance. For instance, the LOD is as low as 0.13 ppbv, the RSD is 1.78%, and the linearity is 0.999 (R2) for H2S, suggesting Unibead 1S is better than Molecular sieve 5A in H2S preconcentration. Unibeads 1S also showed better efficiency than Tenax TA for C2H5SH, and comparable performance for CS2、DMS and DMDS. With Unibeads 1S, the RSD for C2H5SH、DMS、CS2 and DMDS is better than 1.76%, the linearity is greater than 0.995, and the LOD (3σ) for DMS、CS2 and DMDS is below 0.11 ppbv. As a result, Unibeads 1S can replace Molecular sieve 5A and Tenax TA as the better choice for online preconcentration of ambient RSCs.
Having proven the performance of Unibeads 1S, a thermal-desorption (TD) GC-PFPD was used to on-line monitor the ambient RSCs. Grab samples collected from potential sources of RSCs were also analyzed by TD GC-PFPD and the results were reported.
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