I don't know whether your SGE valve is mounted inside the oven or not. On
some systems they are mounted inside the column oven. If you use your GC
at high temperatures, this decreases the lifetime of the parts of the SGE
valve. It's a relatively simple job to move this valve so it is mounted
outside of the GC (make sure it's not soo near the injector) so the fused
silica goes through the hole in the GC wall and then to the valco
tee/cross piece.

Just to echo the other post on this, the ferrules on the tee-cross piece
are also another point which could well lead to this problem.

Simon


> Dear colleagues,
>
> 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
> now.
>
> Sorry if I gave to few technical details, I promise to improve myself..
>
> Regards,
>
> Tim Sobolevsky, PhD
> Senior Analyst
> Moscow Anti-Doping Center
> Russia
>
>