Dear Geoff,

you may want to read the following papers:
Glaser, B., Amelung, W. 2002. Determination of 13C natural abundance of
amino acid enantiomers in soil: methodological considerations and first
results. Rapid Communications in Mass Spectrometry 16, 891-898.

Schmitt, J., Glaser, B., Zech, W. 2003. Amount-dependent isotopic
fractionation during compound-specific isotope analysis. Rapid
Communications in Mass Spectrometry 17, 970-977.

Meier-Augenstein, W., Watt, P. W., Langhans, C. D. 1996. Influence of gas
chromatographic parameters on measurement of 13C/12C isotope ratios by
gas-liquid chromatography-combustion isotope ratio mass spectrometry.
Journal of Chromatography A 752, 233-241.

Meier-Augenstein, W. 1997. The chromatogrphic side of isotope ratio mass
spectrometry: Pitfalls and answers. LC GC International, 17-25.

Kind regards


Dr. Bruno Glaser
Lehrstuhl fur Bodenkunde und Bodengeographie
Universitat Bayreuth
D-95440 Bayreuth
Phone: ++49-921-552254
Fax: ++49-921-552246
Email: [log in to unmask]

  -----Ursprungliche Nachricht-----
  Von: Stable Isotope Geochemistry [mailto:[log in to unmask]]Im
Auftrag von Geoffrey Garrison
  Gesendet: Donnerstag, 15. Mai 2003 00:11
  An: [log in to unmask]
  Betreff: [ISOGEOCHEM] ISODAT problem

  We recently installed a new Finnigan MAT253. After the install, we
discovered that the isotopic results being reported by ISODAT were varying
as a function of sample size. I would normally chalk this up to incomplete
sample combustion or acidification, but these samples were coming directly
from our CO2 standard tank. Finnigan has been totally unable to even suggest
what the problem might be or how to pursue it. I think the problem is in how
ISODAT (ver. 1.5) is processing the output from the 253, but it's not at all
clear from the manual how to troubleshoot such a problem. There is a -0.6
per mil reduction in d18O and a +0.3 per mil increase in d13C on CO2 samples
from the same tank ranging between 10K mV and 40K mV in size. Any advise or
tales of similar experiences would be greatly appreciated.



  Geoffrey Garrison, Associate Researcher

  Department of Earth and Space Sciences University of Washington
  63 Johnson Hall, Box 351310

  Seattle, WA  98195

  (206)616-8763, office

  (206)543-6327, lab

  [log in to unmask]