Penny:
I just went through something like this recently. I had the retention times
increase by 40 seconds over the course of one run. I had tried baking out,
trimming column ends, but to no avail. I tried increasing the GC temp and
that sped up the retention times, but obviously was not a solution. I
finally replaced the GC column and was astounded at the difference. I
probably should have done it months before. Even though the new column
(Agilent GS-Q, 30m, 0.32mmID) was longer, the retention times were far
faster than on my original column (Varian Poroplot-Q, 25m, 0.32mmID), even
when it was new. Reason for change in column type: price. About $400 cheaper
for the Agilent.
Hope this helps.
--Alison
________________________________
Alison Pye . [log in to unmask]
Stable Isotope Lab Coordinator
CREAIT . TERRA Facility . Stable Isotope Lab
Alexander Murray Building
Memorial University of Newfoundland
St. John's, NL . Canada . A1B 3X5
ph: (709) 737-3217 . fax: (709) 737-2589
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Penny Higgins
Sent: June 7, 2010 9:45 AM
To: Alison Pye
Subject: Sudden increase in GC elution times
Hi all,
Just a quick question.. I think I already know the answer.
We run carbonates on a Deltaplus XP in continuous flow mode via a Gas Bench.
Rather suddenly, the elution times for our sample peaks increased by
about 50%. When I say suddenly, I mean one analysis was fine and the
next and all subsequent were delayed. I've baked out the GC, cleaned
the valco valve, cleaned one of the two nafion traps and replaced the
sample needle thinking that maybe there's just a little clog
somewhere. Alas, to no avail. The temperature in the GC oven is the
same as it has been prior to the elution time change (verified by an
independent thermocouple), so I suspect that there's junk in the GC
and it's time to replace it. Ugh!
Can anyone think of anything else that may be slowing down elution
times on the sample side? Could a clog in the caplillary leading from
the sample open split to the source cause such a slow down? Could a
messed up nafion trap cause this? ...Or is it probably the GC column
as I suspect.
Does anyone know of any way to 'fix' a GC column?
Thanks,
~Penny
*******************************************************************
Dr. Pennilyn Higgins
Research Associate
"SIREAL"
Stable Isotope Ratios in the Environment Analytical Laboratory
Department of Earth and Environmental Sciences
University of Rochester
227 Hutchison Hall
Rochester, NY 14627
[log in to unmask]
Office: 209b Hutchison Hall Lab: 209 Hutchison Hall
Voice : (585) 275-0601 Outer lab: (585) 273-1405
FAX : (585) 244-5689 Inner lab: (585) 273-1397
http://www.earth.rochester.edu/SIREAL/index.html
*******************************************************************
|
