Hi Lehmann,

I don't know whether you already narrowed down the location of the problem, but
if I were you, I would disconnect the GC column from the furnace and connect to
another detector directly, such as FID so that I can know if this is a GC
problem or after the GC.

Good luck, Satoshi
Satoshi Irei
The Centre for Atmospheric Chemistry
York University, 4700 Keele St., Toronto
Ontario, M3J 1P3, Canada
Phone +1(416)736-2100 ext 77033
Fax +1(416)736-5411

Quoting Charlotte Lehmann <[log in to unmask]>:

> We have a Delta V with GCCIII and Trace GC. Last good runs were at the
> end of November with no use until 1/2/08. On 12/21/07, I turned the
> source off since no one would be around during the Winter Holiday. The
> PI turned on the source and geared up to run some samples, but: "On
> Wednesday last week, things looked fine for the first couple of runs
> of the standard, and then something happened between the third and
> fourth injection -- n-alkane peaks became delayed, broader and much
> smaller. (The CO2 Ref on-offs are fine -- meaning the problem lies up
> stream of the ref inlet.) My initial thought was a leak somewhere.
> Mass 40 was higher when back-flush is not on, suggesting a leak.
> However, I have checked for leaks everywhere using the leak detector
> and snooping with argon (while monitoring mass 40) and there is no
> sign of a leak anywhere. Backflush valve flows are fine. I have
> installed new septa, and re-oxidized the furnace...still no
> improvements."
> I checked, at her request, to see if a mass scan gave an indication
> that the oxidation or reduction furnace was spent. The mass scan, in
> "straight mode" with back-flush and dilution OFF, looks the same as
> with them on, and the masses all appear normal in size, shape, and
> relative proportions. They look very similar to the mass calibration
> scan done on 10/25/07 when the filament was replaced and the
> instrument tuned through the Conflo III (on the EA side).
> I even scanned without REF CO2 in, both "straight" and "not straight"
> modes. Peaks are small, no leaks apparent.
> Any thoughts, suggestions, etc. would be greatly appreciated.
> --
> Charlotte Lehmann
> Assistant in Instruction
> Bates College
> Department of Geology
> 206A Carnegie Science Building
> 44 Campus Avenue
> Lewiston, ME 04240
> Phone: 207-786-6485
> FAX: 207-786-8334