Hi Misuk,
Does your TCD trace show the same problem peak? This could really tell
you if the problem is with the EA.
The only similar occurrence for me has been from 2 samples dropping
relatively close to one another, in the same analysis. Any chance your
autosampler is dirty?
When you baked the GC was the EA at full flow and disconnected from your
IRMS? The Haysep Q typically has a regeneration temperature of 200C, so
it might be worth baking your column again at a higher temperature. I
use the max the Costech will go to (110C), and run it 24h at full flow
vented to the room. This will prevent the junk from going to the
conflo.
You could also check backgrounds connected to the conflo without the EA
connected to see if there is possibly a contaminant in any of your
gasses.
Some other checks could be trying the other O2 loops and running
with/without dilution, just in case you have an issue with the splitter
valve in the Conflo.
Good luck,
Ben
Benjamin Harlow
Manager, Stable Isotope Core Laboratory
Washington State University
School of Biological Sciences
G-81 Eastlick
Pullman, WA 99164-4236
Office: 509-335-6161
Lab: 509-335-6154
Fax: 509-335-3184
Laboratory for Biotechnology and Bioanalysis (LBB2) Stable Isotope Core
http://www.isotopes.wsu.edu
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of Misuk Yun
Sent: Thursday, March 11, 2010 2:10 PM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Time for GC column (EA) replacement?
Hi,
I am working with Delta V Plus + Costech EA for N and C isotope
measurement.
Last week, a few samples (one batch) showed a second peak (mass
44/45/46),
starting ~100-150 seconds after the end of sample CO2 peak. So, this
peak
happened to overlap with Ref CO2. The sample size was not big, ~0.3 mg
with
micro O2 loop.
Now, I have all new chemicals (oxidation/reduction/water trap). There is
no
air leak; background of mass 28, 29 and 40 are all low. Mass 18
intensity
used to be ~300 - 500 mV, but, now it is over 1200 mV (fluctuating
between
1200 and 2000 mV). Mass 32 intensity (~300 mV) is higher than the
used-to-be
(~30-60 mV). I baked GC column at 100C two nights, but they don't reach
what
they used to be. When I ran a few Sn blanks, the second peak (very
broad) is
still there.
When I closed the needle valve to separate IRMS from EA, the backgrounds
dropped (even mass 18 and 32). So, this is from EA.
Where is the second peak (44/45/46) from? Is this N2O, which also has
mass
44/45/46? Does this mean the end of GC column? Our GC column is only 2
years
old.
Any advice (^_^)??
Thank you.
Misuk
-----------------------
Misuk Yun (M.Sc.)
Manager, SIFIR (Stable Isotopes For Innovative Research) Lab &
Geochemistry
Lab
Department WHMIS coordinator
Department of Geological Sciences
Wallace Building
125 Dysart Rd.
University of Manitoba
Winnipeg, Manitoba R3T 2N2
CANADA
Phone: 1-204-474-8870
Fax: 1-204-474-7623
E-mail: [log in to unmask]
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