We use a variety of gases, pure and mixtures, mostly UHP grade, which we
obtain from Matheson-Trigas.  Upon receipt of a new cylinder, we measure dew
point by flowing gas through a portable dewpoint meter (Xentaur model XPDM),
which is a capacitance type moisture meter that has a sensitivity down to
-100 degC.  We routinely observe dewpoints in the -70 to -80 degC range,
which is sub ppm.  We have not found a need to place in-line moisture
filters on any of our UHP 1A cylinders.

Steve Balsley
Sandia National Labs



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I am setting up an IRMS lab and was wonder what experience people have had
using in line filters on their supply and standards gases. In my past
experience with GC/MS systems, even using HP and UHP gases (4.5-5.0) it was
always recommended to have moisture traps on the gases. Has anyone
experienced problems doing this on a EA-IRMS system? Or do you assume that
the gases are ultra-clean from the supplier and leave it at that? An
recommended filters to get or stay away from for IRMS work? Thanks,

Howard
Howard Sanford
Stable Isotope Ratio Mass Spectrometry Lab
919-513-3039
North Carolina State University
Dept. of Soil Science
Box 7619
Raleigh, NC 27695