Hello,

I am a new graduate student at Syracuse University, working on a  
multi-tracer approach to local groundwater problems. Among these  
tracers are oxygen/hydrogen isotopes, which we measure using a water  
equilibration bath (GFL 1086;  24 samples (3 rows of 8 bottles); 24  
Deg C; 8 hrs equilibration) connected to a Finnigan MAT252 mass  
spectrometer.  Despite great efforts, I keep having the following  
problems (with great consistency….):

1.  The first sample bottle of each row (samples 1; 9; 17) yield  
consistently bad numbers (several per mil off), despite gas pressure  
readings being ok.

2.  The spread in d18O values for samples from the first row of  
bottles (samples 1-8) is very large, with variations of up to 1.5  
permil.  The variations of samples in rows 2 and 3 (samples 9-24;  
except 9 and 17 - see above) are much smaller (within 0.3 permil).  
Changes in equilibration times does not influence or improve this  
pattern (tests were done for 4, 5, 6 and 8 hours).

3. Another pattern we consistently see is a slight but steady increase  
in isotope values for each individual row (it goes down again at the  
first sample of the next row), resulting in a cyclic pattern.

4. Last but not least, once in a while the 24 sample bottles seem to  
have very different amounts of gas in them but fortunately, this does  
not happen very often!

Has anybody experienced similar problems?  Or even better: does  
anybody know how to approach/solve any of these problems?

I truly welcome any insights and suggestions on how to improve my  
oxygen isotope measurements with the existing equipment.

Best regards,
Mimi


-- 
Mimi (Soumitri Sarkar)
Graduate Student and Teaching Assistant
Room #212, Heroy Building
Department of Earth Sciences
Syracuse University