Shaun, I don't know anything about using Drager tubes, but I seem to recall a study a while back (approx. 2000, maybe?) that ran into the same problem that you have. They solved the problem by putting some silver phosphate into a cold finger on a vacuum extraction line, and then froze the gas sample into the cold finger and let the sample react for a few minutes at room T, presumably to form silver sulfide and phosphoric acid. I recall reviewing the paper, and making sure that the authors included some additional details about this technique to clean up their gas samples (it wasn't a methods paper) Unfortunately, I can't remember the authors, nor do I have a copy of the paper that I can find - maybe another Isogeochemer (who's younger and whose memory isn't shot like mine apparently is) might recall this paper? Cheers, Simon >Dear all, > >We are trying to separate H2S from CO2 gas >samples in a vacuum line, prior to isotopic >analysis of carbonates which are variably mixed >with different proportions of different sulfide >minerals, particularly As-rich pyrite (which >seems to dissolve very readily in phosphoric >acid). > >I read with interest some of the discussion from >a few years ago on the Isogeochem list on this >topic, particularly with regard to the potential >use of Dräger tubes to remove H2S from CO2 >samples. > >Does anyone have practical experience with >fitting and using Dräger tubes in a vacuum line >for this purpose? > >If so, could you tell me: > >(a) what model of tube you used (Drager >manufactures about 8 different tubes for H2S >detection) > >(b) What the OD of the tubes are, in order that >we can try to rig something to fit the tubes to >our existing 1/4" and 1/2" Ultratorr fittings. > >(c) What your "procedure" was to allow the tubes >to remove the H2S gas, i.e. did you trap water >before or after the Dräger tube, how long did >you allow the gas to interact with the Dräger >tube prior to capture of the CO2 for subsequent >analysis etc. > >Are there any other practical methods or >techniques that people have used? Ideally, we >are looking for a method that can readily be >used for hundreds of samples. > >Cheers, >Shaun > > >--------------------------------------------------------- >Shaun Barker >Post-doctoral Fellow >Mineral Deposit Research Unit >Department of Earth and Ocean Sciences >University of British Columbia >Vancouver, BC Canada V6T 1Z4 > >Tel: (+1) 604 822-1874 >fax: (+1) 604 822-6088 > >email: <mailto:[log in to unmask]>[log in to unmask] >---------------------------------------------------------- -- ***** Simon Poulson Research Professor Dept. of Geological Sciences & Engineering MS-172 University of Nevada - Reno 1664 N. Virginia St. Reno, NV 89557-0138. USA (775) 784-1104 Fax: (775) 784-1833 [log in to unmask] http://www.mines.unr.edu/isotope/simonhome.html *****