Another tip:  Before running dD with the HDevice, perform all of the 
d18O analyses first.  This will allow you to place samples with similar 
dD values near one another in the sequence, thereby reducing the memory 
effect of one sample on the next.


On Feb 6, 2007, at 12:11 AM, Geldern, Robert van wrote:

> Hi Georges,
>
>> This has been described as "carryover" and "source conditioning",
>
> You may check the archives also for memory effect. We do not run a
> TC/EA with solid samples but see a similar effect for dD on
> the H/Device (water). This effect results from a "memory" of the last
> samples
> in your reactor, not in the MS. I have no clue if the source of this is
> the
> reactor filling or the glass walls of the reactor tube (or both).
>
> In genreal, you have three way to deal with this:
> 1) Inject your sample three times and discard the first (two?) values.
> (costs time and money)
> 2) Inoculate your reactor with one or two "dummy" injections of your
> sample before measuring it (saves time)
> 3) Run your samples in duplicates/triplicates and make a
> mathematical post run correction of the data by substruction of 0.5
> to 1% of the difference (jump) between your samples (n) and the
> sample before (n-1) and/or about 0.05% of the difference between (n)
> and (n-2). The acutal value of the percentages have to be determined
> in each run by looking at large jumps of your standards (e.g. SMOW-
>> GISP or house standards in this range).
>
> I can send you my excel speadsheets on request.
>
> regards,
> Robert
>
>
>
> --
> Dr. Robert van Geldern
> Section 3: Geochronology and Isotope Hydrology
> Leibniz Institute for Applied Geosciences (GGA-Institute)
>
> GEOZENTRUM HANNOVER
> Stilleweg 2
> 30655 Hannover, Germany
>
> Phone: +49-(0)511-643-2313
> Fax: +49-(0)511-643-3665
> mailto:[log in to unmask]
>
>
>
-- 
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