<http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/efnhh.htm>
Hi Bill,
I fully agree with you on the subject of good reactor "husbandry", which ties in with the comment Gerard made earlier. Whenever possible we avoid running mixed samples (i.e. samples of a different matrix or nature) on the same reactor and we refurbish our reactors painstakingly between runs. Usually we have two complete reactors ready to go in the drawer plus one operational in the TC/EA.
I too noticed the yellow to green crystall formation on the outside of the glassy carbon tube (and so have others). This matter has been the subject of some discussion on the list and if memory serves the consensus was it's not sample related but some yet to be explained "sublimation" of ceramic tube material in the hot zone.
Fresh out of the reactor the crystals are almost impossible to remove but left on the bench for a few days the crystals fall off when tapped forcibly but not too forcibly.
I haven't noticed the increased rate of reactor deterioration with sulphates you mention but that's most likely due to the low number and the low frequency of sulphates samples in our lab. Good to know that's something to be mindful of.
Best regards,
Wolfram
________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Bill Showers [[log in to unmask]]
Sent: 27 July 2007 22:38
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] NBS-127 on TC/EA
Wolfram,
We have also routinely run BaSO4 in the TCEA in my lab with out any problems for over 9 years.
I think the problems others describe such as in the Straight et al article is caused by running too many samples without changing out the graphite tubes or reusing graphite granules too many times.
Since we have been so concerned with background levels, we change everything out when backgrounds are above 100 mv (which is every 4x to 5x). Thermo recommends 200 mv, but we seem to get better reproducibility <100 mv.
I notice that the carbon and ceramic tubes need to be changed more often as do the carbon granules when running BaSO4 as opposed to not running BaSO4 as a calibration std for oxygen, and that a yellow crust can build up on the graphite & ceramic tubes.
We have gone to using different sugar standards (sucrose, fructose, galactose), they seem to cause less wear on the graphite tubes and granules and have excellent reproducibility. But do not have as low a O-18 value as BaSO4. Does anyone have an alternative O-18 std for pyrolysis for the TCEA that has ~+10 per mil value other than BaSO4?
We buy the replacements parts from IVA, if you change out things regularly you should not have the types of problems that Bill Straight had (at least we never have seen anything like what he describes).
Perhaps more than 2 cents worth.
Best of luck,
Bill Showers
At 01:20 PM 7/27/2007, you wrote:
Dear Greg,
We have run sulphates on our TC/EA without any problems. To be honest, we were pleasantly surprised how unproblematic the analysis was and how good the results were (right on the money) considering what problems people reported for pre-TC/EA methods.
In anticipation of problems we run sulphates with and without the addition of graphite or milled charcoal (chemistry grade not BBQ) and saw no difference in the results.
Same as you we figured the silver was taken care of the sulphur since subsequently run organic house standards (i.e. on the same reactor) showed no signs of being adversely affected.
Best,
Wolfram
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Dr W Meier-Augenstein
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Environmental Forensics & Human Health Research Group
EERC, S.P.A.C.E.
Queen's University Belfast
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Email: [log in to unmask]
URL (Isotope Lab): http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/siff.htm
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________________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Cane, Greg [[log in to unmask]]
Sent: 27 July 2007 18:09
To: [log in to unmask]
Subject: NBS-127 on TC/EA
Anyone ever use NBS-127 (Barium sulphate) on their TC/EA? I'm a little
worried about sulphur generation, however I'm assuming the silver
capsules will take care of sulphur generation during the reaction. Any
thoughts, advice?
Greg
Greg Cane, Lab Manager
W.M. Keck Paleoenvironmental & Environmental Stable Isotope Laboratory
University of Kansas, Dept. of Geology
Multidisciplinary Research Building
2030 Becker Drive, RM 130
Lawrence, KS
66045
Tel: 785-864-7750
Fax: 785-864-1906
William J. Showers
Dept of Marine, Earth & Atm Sciences
North Carolina State University
Raleigh NC 27695
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