H2S, RS in methane

[puff]

I need to determine total sulphur (H2S and mercaptans) in CH4 using packed sulfinert column and FPD. Sample is taken and hold in 25l Tedlar bags. I know that Sulphur total concentration is <1ppm, but must be determined more precisely by chromatografy. Detector response of H2S is very poor, so more advanced solution is needed. I think of selective sulphur compounds trap and thermal desorption of adsorbed mixture to the column. I look for a proper trap which can be used in my analysis, or other ideas.

Thanks in advance for any suggestions.

[chromatographer1]

The application you describe has been done for decades by multidimensional chromatography and FPD or sulfur chemiluminescence detection.

It is measured in three peaks, H2S, COS, and Mercaptans+ peak.

The sample loop and columns use teflon columns instead of sulfinert metal columns, although you did not say what kind of wool you are using, but it must be very clean and inert.

You might be able to perform this analysis on a thick film methyl silicone capillary column which many companies sell, Supelco, my company is one of these suppliers.

I would suggest that you call technical service of the supplier you choose and follow their advice.

best wishes,

Rod

[AICMM]

Puff,

A trap is not likely to work for this application for two reasons. First, the H2S is very light and likely to breakthrough at very low volumes and, second, the sulfur compounds are very reactive and run the risk of reacting with the trap. Rod's comments about teflon and inert systems are very important since these are very reactive compounds.

My suggestion (after looking at system cleanliness) would be to look at alternative detectors for this application (although I am completely biased in this statement.) The PID, PDD or my own DBD detector would do very well for this application, especially if you don't have to measure COS. Your system still has to be very clean but H2S and the mercaptans have delightfully low ionization potentials (less than 10.5) which makes them ideal for these other detectors. The only other issue is that you have to have sufficient separation from the hydrocarbon background since many of the components in natural gas will also show up on these detectors.

This is an application I am very interested in and I would be delighted to discuss it with you further if you want to contact me through my web site.

Best regards.

[philippem]

Hi Puff,

You could contact Varian in Middelburg (Netherlands). They supply systems ( columns and equipment) for these kind of analysis. They can advice you

Varian chrompack international B.V.
PO box 8033
4330 EA Middelburg
Fax: 0118-633118
http://www.varianinc.com

regards

philippe