Hi Penny,

We had this issue with some waters from alkaline lakes in Burma.  The  
basic solution (or solution to the basic problem) is to add  
acid--100% H3PO4.  I think the method is actually described in the  
Gasbench Manual, but you would also need to make sure that the CO2  
evolved during acidification has completely evolved before flushing  
with your CO2-He mix, and that the water has fully equilibrated with  
the now Calcium Phosphate brine.

Best,

Jonathan.

Jonathan Wynn
Department of Geology
University of South Florida
4202 E Fowler Ave, SCA 528
Tampa, FL 33620
(813) 974-9369
[log in to unmask]
http:shell.cas.usf.edu/~jwynn



On Aug 4, 2006, at 2:30 PM, Penny Higgins wrote:

> Hi all. I have a curious problem. I've been doing headspace  
> analyses for d18O of water samples using the Gasbench in continuous  
> flow mode on our Delta plus XP.
>
> A few samples yielded negligible peaks. I re-ran them, and still no  
> measurable peaks. I decided to check the pH and have found that the  
> samples that won't run are all at about pH 12. Presumably, the CO2  
> gas that I'm flushing with is going into solution in the water  
> rather than remaining a gas in the headspace and exchanging oxygen  
> like good gasses should.
>
> I think I need to neutralize the waters, but I'm not sure how to do  
> it without affecting the oxygen values of the water.
>
> Has anyone else dealt with this problem? What did you do about it?  
> If need be, I could run the oxygen analyses using our TC/EA, but  
> since I've run all the other samples in this set by headspace  
> equilibration, I'd like to run them all this way.
>
> Thanks,
>
> ~Penny
>
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