At 10:09 13.05.1997 -0800, you wrote:
>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])
>
Dear Martin,

I used vacutainers for routine analysis of water samples for their delta 18O.
I used 1ml sample and 500µl CO2 with an equilibration time of 24 hours. Even
if I equilibrate for 27 or some more hours I did not observe any
fractionation. Furthermore I used the same septum for three analyses, each
analyses was repeated 3 times, so I ended up with 9 holes in my septum
without any effect.
Hope this will help!
For further questions I am here.
Bye
        Andreas
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Andreas Lücke
Forschungszentrum Jülich
Institut für Chemie und Dynamik der Geosphäre ICG-4
Abt.: Isotopengeochemie und Paläoklima
D-52425 Jülich

tel.: +49-(0)2461-61-4590
fax: +49-(0)2461-61-2484
e-mail: [log in to unmask]

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