Dear Robert,

What is the additional uncertainty introduced by your correction procedure
as described under 3)? For certain such a procedure makes the measurement
less precise...

Pier.
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> From: "Geldern, Robert van" <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
> Date: Tue, 6 Feb 2007 08:11:38 +0100
> To: <[log in to unmask]>
> Conversation: [ISOGEOCHEM] How do enriched samples affect reproducibility?
> Subject: [ISOGEOCHEM] AW: [ISOGEOCHEM] How do enriched samples affect
> reproducibility?
> 
> 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
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>  
>