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Tim,

Do you have an SGE valve on your Delta Plus? It is possible to overtighten
the joints: the vespel seals squeeze the capillaries so that the gas flow
is disrupted. In this situation you get slow response and tailing on both
sides of the peaks. The SGE valve won't explain the dual inlet mode, but it
is worth checking.

Janet Gabites

At 08:47 AM 6/28/2005, you wrote:
>Thanks Wolfram and Shuhei for your responses.
>
>Just to clarify:
>
>I have peak tailing of CO in both continuous flow and dual inlet modes,
>so I have ruled out the peripheral devices (along with GC and Conflo)
>as the cause of the tailing.  My turbo pumps all show green lights
>indicating there is no problem there.  I have also baked out my inlet
>valve to get rid of moisture that had collected there when I vented the
>machine, with no success.  I always view the position of my filament
>with the trap removed to ensure that it is properly aligned.  I also
>run with my source heaters on all the time.
>
>But I have seen this problem before when I cleaned the ion source, and
>I tried several things back then to solve it: change filaments, change
>ion exit slit, clean ion source again, but none of these had any
>effect.  Over time the tailing disappeared though...very odd.
>
>This led me to the following conclusions about what could be causing
>the tailing: (1) could there be some sort of residue on the ion source
>plates from my cleaning procedure that is interacting with the CO (my
>final step is to sonicate the source in acetone then bake at about 80C
>to dry before reinstallation...maybe the acetone wasn't pure enough at
>99.5%).  I will try 100% ethanol next time; (2) the bead blasting of
>the ceramics and failing to anneal them afterwards...could porosity
>have been exposed that is sealed off during annealing?  I have a set of
>ceramics on order to test this.

Janet Gabites,
Stable Isotope Facility,
Pacific Centre for Isotope and Geochemical Research,
Department of Earth and Ocean Sciences,
The University of British Columbia,
Vancouver, B.C. V6T 1Z4
ph 604-822-6654
fax 604-822-6088
http://www.eos.ubc.ca/research/pcigr/PCIGR.htm