At 08:59 AM 11/8/96 GMT0BST, you wrote:
>Hi, 
>
>I am currently measuring delta 13 C in organic matter, mostly 
>cellulose, some sediments. As an internal standard, I use IAEA 
>pure cellulose standard, originally distributed for the standardization 
>of radiocarbon dating labs. 
>
>These labs measure the 13 C routinely as well, but 
>usually with poor precision (they need the information as background 
>for age determination, but 1/2 ppm difference in 13 C doesn't make 
>much of a difference for the age anyway). So the methodology is often 
>a bit "sloppy", producing large standard deviations.
>
>I have a published list with delta 13 C values for the IAEA cellulose, 
>measured by radiocarbon labs,  but it shows a wide spread of values
>- as I expected. In contrast, my own measurements all produce very 
>nearly the same d 13 C - the material is in fact very homogeneous.
>
>My question: Has any stable isotope lab measured the material for 
>13 C specifically, so that I can compare my results with theirs? If 
>not, would anybody be willing to do some measurements for establishing 
>a more exact d 13 C value? I could provide the standard.
>
>And: Is there another suitable standard material for organic carbon, 
>preferably in the form of cellulose? I think some people use some 
>organic acid (or so) for that purpose, but I'd prefer something that is 
>processed exactly as my samples.
>
>
>Frank Pawellek
>
Dear Frank:

Our lab has been using NBS-22 oil (delta13C, -29.80) as working standard for
organic carbon isotope ratio measurement for over ten years. It always gives
constant values. We like to do some measurements for your cellulose
standard. Please send in the sample. One analysis needs 20mg material

Dachun Zhang
Stable isotope lab supervisor
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