Karine:
Back in July, 2003, we began running coccolith samples that had been
stored in ethanol rather than water, to avoid dissolution, with our
Optima-MultiPrep, also at 90°C. Although we dried the samples in an
oven before analysis, we discovered that the ethanol did not always
completely evaporate. Those samples still containing ethanol
resulted in V-shaped 46/44 traces, while the 45/44 traces were
perfectly flat. NBS-19 samples run immediately before and after the
coccolith samples were perfect. Of course, ethanol has a mass of 46,
so this all made sense. We subsequently rinsed the coccolith samples
3 times with deionized water prior to drying in an oven at 70°C for
16 hours and never had a problem with V-shaped 46/44 traces again.
Is there a chance this is the cause of your problems?
Steve
>Dear Listmembers,
>
>We recently experienced a problem when carbonates analyses are run
>on our Multiprep-Optima :
>the 46/44 ratio traces are v-shaped instead of flat,
>the 18O precision is bad (around 0.020 instead of lower than 0.008),
>and delta18O values of NBS19 can differ from 1 per mil in the same batch.
>
>I've checked all the valves of the Dual-Inlet and the Multiprep for
>air leaks and cross seat leakage, all the valves are OK.
>When I run stabilities and linearities (with the same CO2 gaz in all
>the DI), traces are flat and values are close to zero, so the DI
>seems to be OK.
>I've checked the water trap and the 2 cold fingers for finding
>contamination, and there is none.
>The bath is equilibrated at 90°C, the needle is brand new.
>I've tested 2 different acids, and the result is always the same.
>
>Have you ever encountered this kind of problem, and found an
>explanation ? because I'm running out of ideas now...
>
>Regards,
>
>Karine
>
>--
>*********************************************************
>
>Karine CHARLIER
>Environnements et Paleoenvironnements OCeaniques
>UMR CNRS 5805 EPOC
>Universite Bordeaux I
>Avenue des Facultes
>33405 TALENCE Cedex
>FRANCE
>
>Tel : 0 (33) 5 40 00 83 62
>Fax : 0 (33) 5 56 84 08 48
>E-mail : [log in to unmask]
>Web : http://www.epoc.u-bordeaux.fr/
>
>********************************************************
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