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Hi Tim,


As I mentioned, annealing the ceramics after cleaning by baking them in a
muffle furnace is definitely a must.

What intrigues me is that you mention fronting and tailing of the peak,
unless this just seems more pronounced because the peak / signal has become
much smaller.

What are we looking at anyway; CO peak from TC/EA or CO pulse from ConFlo
ref gas?

If it's the latter, then, yes, we can exclude TC/EA incl. GC column. In
which case, Shuhei has a point. Your loss in sensitivity (which makes the
"normal" tail look more pronounced) may be the result of a source
mis-alignment.

Despite the fact that the source can only be inserted into the analyzer
housing one way, there is still a wee bit leeway where the alignment of the
gas inlet is concerned. The two holes have to be aligned perfectly. Even a
partial eclipse results in poor sensitivity and all manner of strange
phenoma caused by the disruption of the gas flow into the source.

Try this: make a not of the signal for the CO pulse as delivered from the
ConFlow; power down the system and vent; apply two marks on the source
flange and the analyzer housing so they are in line (felt pen or similar);
loosen the source flange bolts ever so slightly to permit "wiggeling" of
the source; gently rotate the source flange (bolts in!) clockwise and
counterclockwise to see if your original position represents 12o'clock as
it were and adjust accordingly. For example, if you find there is no slack
clockwise but a teensy weensy bit of movement in the opposite direction,
aim for a final position halfway counter-clockwise (your felt pen mark
should help) and tighten the bolts again. Power up and see what signal size
you are getting now.

Lastly, there is always the possibility you might have to retune (refocus)
the source (but I sort of took it as read you had done that already what
with having the source taken apart, cleaned and all). 8^))


Best wishes,

Wolfram



On Jun 28 2005, tcp121 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.
>
> Thanks again...
>
> Tim
>
> -----------------------------------------------
> Tim Prokopiuk
> B. Sc. Geology/Technician
> Saskatchewan Isotope Laboratory
> Room 241
> Department of Geological Sciences
> University of Saskatchewan
> 114 Science Place
> Saskatoon, Saskatchewan, Canada
> S7N 5E2
> Phone:  (306) 966-5712
> Fax:            (306) 966-8593
> Email:  [log in to unmask]
>