as a newbie to the field of GCC-IRMS, I may not understand some basic things,
but I have found a leak in my system that I cannot explain nor cope with it.
The system is Trace GC / Combustion Interface III / Delta V Advantage,
intended for analysis of steroids.
When switching from straight mode to the backfkush, if open split remains "in",
I see a short but intense leak. Monitoring mass 40 at cup3, the intensity may
reach 1.5V for a moment of several seconds (mass 28 at cup3: up to 10V).
The intensity depends on how long the backflush valve was closed (the signal
maybe 300 mv Ar or something if I close it for 10-20 sec), and the time lag
between backflush opening and seeing the leak in mass spec is ca. 5-7 sec.
I disassembled the valve and replaced the vespel seat and PTFE seal.. sprayed
Argon near every suspicious place.. closed the restriction capillary at SGE
valve with septum.. connected the valve to the argon tank instead of
pressurized air - all this did not change a bit.
Additionally, I 've tried to exclude the GC part by making helium to flow as
follows: sge valve -> reduction furnace -> nafion -> open split. All in vain until
Sorry if I gave to few technical details, I promise to improve myself..
Tim Sobolevsky, PhD
Moscow Anti-Doping Center