Issam:

If I'm reading your message correctly, you are taking the proper
steps to remove organic matter from your low-carbonate samples.  I
prefer sodium hypochlorite, but some prefer hydrogen peroxide.
Others prefer to roast their samples.  Just last week we had a
discussion of this on the list.  You can check the archives over the
past several years for extensive discussions of pre-treatment methods.

I, too, use an Optima-MultiPrep combination and have had no problem
with running low-carbonate samples, although most of the samples we
run are pure carbonate.  What specifically are you concerned about?
Are the delta values of your samples not what you expect?  Have you
tried the pre-treatment on standards to make sure your method is
proper?  If the organic matter is not completely removed, or, if
using hypochlorite, you don't rinse the samples well enough with
deionized water, perhaps you have some contaminants building up in
the source or flight tube of the Optima, especially if all of those
10,000 samples were low-carbonate ones.

Perhaps you can give us more details of your problem.

Steve


>Hello all,
>I am working since 4 years ( 10000 samples from 1999) with Optima coupled
>with Mutiprep system from Micromass. I have problem with somes samples a
>low carbonate ( samples with low carbonate (3 -7%) can be a potential
>problem !!!)
>It's necessary to remouve all organic mettres ...OK ( nitrogen compounds,
>salts and clays ) but it's very difficult and I think it's impossible to
>use this system for determination 18O and 13C from carbonate .
>I use H2O2 or Hypochlorite for removins organics metters by oxydation.
>>Any advice in this regard would be most welcome!
>
>>Thank you,
>>I.Moussa.
>>
>>

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