If I can assume that you are only looking at Sulphur on the IRMS, then do you have a short Teflon GC column packed with HayeSep Q? Do you have 2mm Teflon tubing connecting the bottom of the combustion/reduction reactor to the water trap? When running Sulphur, I get as much of the stainless steel out of the system as possible. I also replace the stainless steel line from the bottom of the water trap to the input to the GC column oven and from the outlet of the GC column oven to the detector bulk-head fitting. I will replace the two 2mm stainless steel lines inside the GC column oven with Teflon. In some severe cases I have replaced the line from the TCD to the Vhe outlet and the transfer line from the outlet to the conflo.
I realize that this is a lot of work, but I trust you will be surprised at the positive results. With the use of Teflon tubing please be sure to check it periodically for debris or carbonization. Also, any pinches in the tubing can lead to some erratic results. If you are not already doing so….increase the GC column temperature to 100 °C for better peak shape and reduced analysis time. Even with all that I described, you will still have to run 8-10 conditioning samples…, but surely not 30-50.
Jon Cocca, Service Manager
Costech Analytical Technologies, Inc.
I have been running sulphur isotopes now for over a year now, using a Delta V+ mass spec with a Costech EA, but I find that when I put in a new reaction column I need to put through about 30-50 sulphanilamide sample before I start getting good signals, no tailing etc.
Does anyone know how I can reduce the number of conditioning samples before running standards and samples?
I’d like to know other experiences you have, or is this just the norm and I need to expect this with doing sulphur isotope analyses.
Dr Darren Grocke
Department of Earth Sciences