Sampling of gaseous sulfur-containing compounds at low concentrations with a review of best-practice methods for biogas and natural gas applications

• We review the stability of sulfur-containing compounds in standard gas mixtures.
• Trace levels of sulfur-containing compounds exhibit good stability in passivated cylinders.
• Stability of sulfur-containing compounds in commercial sampling vessels is variable.
• There are significant losses of sulfur-containing compounds stored in sample bags.
• We make suggestions to improve the accuracy of measuring sulfur-containing compounds.

The accurate quantification of low-concentration sulfur-containing compounds is essential for the biogas and natural gas industries. We review literature data for the stability of these compounds in standard gas mixtures when sampled in cylinders with different passivations, sample bags, sorbent tubes, solid-phase microextraction and glass sampling bulbs, and we present new data obtained at our three National Measurement Institutes. We show that losses of sulfur-containing compounds are minimized when using passivated sampling cylinders, and the most suitable sorbent material for sampling these compounds is Tenax TA. We also discuss methods for transferring gas from sample vessels to analyzers and give recommendations for the selection of regulators (and other pressure-reducing devices) and transfer lines. Further, we propose approaches that could be taken to reduce or correct for losses in order to provide more accurate measurements of sulfur-containing compounds.