I'll double check it, but I have glass press-fit installed instead of Valco X-piece
(spraying argon over GC parts including the pressfit did not change mass 40
intensity in straight mode).
My unrealistic guess is that once the BF valve in the interface is closed, helium
(due to its fluidity) slowly sweeps out of the valve (no matter how tight are
the connectors; maybe through 0.1x100 restriction capillary) resulting in the
permeation of air inside.
Regards and thank you,
Tim Sobolevsky, PhD
Moscow Anti-Doping Center
On Wed, 18 Jun 2008 13:50:32 -0700, Georges Paradis
<[log in to unmask]> wrote:
>We recently experienced the same symptoms. We traced the leak to the
>x-fitting in the GC. Try replacing the ferrules and reinstall the
>capillaries at the x-fitting.
>Georges L. Paradis
>Analytical Lab Manager
>Marine Science Institute
>Bldg 520, Room 4013
>University of California Santa Barbara
>Santa Barbara, CA 93106
>805-893-7182 (ICPMS lab)
>805-893-3802 (MSI lab)
>[log in to unmask]
>Tim Sobolevsky wrote:
>> Dear colleagues,
>> as a newbie to the field of GCC-IRMS, I may not understand some basic
>> 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
>> I see a short but intense leak. Monitoring mass 40 at cup3, the intensity
>> 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
>> 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..
>> 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
>> Sorry if I gave to few technical details, I promise to improve myself..
>> Tim Sobolevsky, PhD
>> Senior Analyst
>> Moscow Anti-Doping Center