Dear List Members,
Has any one experienced large isotopic fractionation of 18O with
'Vacutainers' during water CO2 equilibrations?  We have been using them for
carbonate reactions and consistently note a > 1 permil fractionation over
24 hours when reacted at 50 degrees.  The fractionation can be corrected
for the first 10 hours and then becomes largely unpredictable.  They appear
to be leaking through the septum.  We have tried sealing them with silicon
with little luck. I would like to do some CO2-water equilibration but am
not sure I trust this method, perhaps there are other brands that do not
leak, or other ways of sealing them etc.  Any advice would be greatly
appreciated.  Also, what would be the minimum time for equilibration of a
.5ml sample in order to reduce the fractionation ?
Thanks for your help
Martin Kennedy ([log in to unmask])



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Martin Kennedy
Department of Earth and Space Sciences
University of California, Los Angeles  (UCLA)
Los Angeles,  CA
90095-1567
Phone (lab)  310-206-7246
              (office)  310-206-4164
Fax  310-825-2779
e-mail   [log in to unmask]