-----Original Message-----
From: Stable Isotope Geochemistry on behalf of Jonathan Karr
Sent: Mon 7/30/2007 9:17 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] NBS-127 on TC/EA
 
Bill,
the problem with BaSO4 goes away with cleaning the glassy carbon tube 
and granules in the reactor, so it is only a problem when you run silver 
phosphate samples immediately after the BaSO4, and the next several 
samples or standards will be affected.  You wouldn't notice unless you 
ran several silver phosphate standards immediately after the BaSO4, and 
watch the variation. It does not seem to permanently affect the reactor. 
The apparent oxygen scavenging effect of the Ba++ also occurs with Ca++, 
another good reason not to run raw samples rather than silver phosphate. 
We too changed things out frequently, but backgrounds are not the issue, 
it's reduced yield and fractionation due to oxygen scavenging by the 
cations.
Jon

Bill Showers wrote:
> 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
>>
>> *********************************
>> Dr W Meier-Augenstein
>> Senior Lecturer
>>
>> Environmental Forensics & Human Health Research Group
>> EERC, S.P.A.C.E.
>> Queen's University Belfast
>> David Keir Building
>> 39-123 Stranmillis Road
>> Belfast, BT9 5AG
>> United Kingdom
>>
>> Tel.: +44 (0)28 9097 4015
>> Fax: +44 (0)28 9066 3754
>> Email: [log in to unmask]
>> URL (Isotope Lab): 
>> http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/siff.htm
>> URL (Research): 
>> http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/efnhh.htm
>> ________________________________________
>> 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
>
> (919) 515 - 7143 Office
> (919) 515 - 7802 Fax
> (919) 515 - 3689 Computer Lab
> (919) 632 - 2283 Cell
> (919) 515 - 7911 Field Lab
>
> Visit our RiverNet Web Site
> http://rivernet.ncsu.edu/
>


-- 
Jonathan D. Karr, Ph.D.
Technical Director, Duke EnVironmental stable Isotope Laboratory (DEVIL)
Duke University Dept.of Biology
3322 French Science Center
Science Drive
Durham, NC 27708-0340

(919) 660-7418
Fax: (919) 660-7425
[log in to unmask]
laboratory website: http://www.biology.duke.edu/jackson/devil/




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