Paul, Thanks for your response. Did you happen to publish any of these results? I have searched everywhere, but can not find any reference for this methodology as related to isotopic analysis. Brian Jones Assistant Research Scientist & Lab Manager Stable Isotope Ecology Laboratory Dept. of Oceanography Texas A&M University College Station Tx. 77843 (979) 845-8916 _____ From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Paul Eby Sent: Thursday, March 24, 2005 11:12 AM To: [log in to unmask] Subject: Re: [ISOGEOCHEM] Pre-concentration and analysis of HC in Atmo We've done a few studies along these lines. As long as the sorbent is strong enough to hold on to the chosen analytes at room temperature (ie not an equilibrium) and you are able to heat the sorbent enough to get the analyte off again, then there should be no appreciable fractionation. Much of this was done with custom built equipment, but really the important factor is finding the right sorbent. Paul Eby University of Victoria At 08:01 AM 24/03/2005, you wrote: Hello All, I was wondering if anyone out there has used the packed tubes to pre-concentrate and a thermal desorption unit to measure carbon isotopes of atmospheric hydrocarbons by GC-C-IRMS. If so, could you tell me the make of the equipment used, if you found any isotopic fractionation from pre-concentrating and/or desorption, and any references to published data from the method. Brian Jones Assistant Research Scientist & Lab Manager Stable Isotope Ecology Laboratory Dept. of Oceanography Texas A&M University College Station Tx. 77843 (979) 845-8916 No virus found in this incoming message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.8.1 - Release Date: 23/03/2005