Dear listmembers,

Thank you very much for the responses to my question about total
N and total C -measurements. I can reply to you the following:

I would first like to add something to the mail from Per Ambus to
Paul Brooks. We also have a good linearity between 25 and 200 µg
for carbon-measurements (total beam - concentration relationship),
and this meets our requirements.

Second, I can perhaps share with all of you how we 'solved' our
reference-problem. Some will say it is probably the most expensive
way, but I think in this case it was quite necessary, since every
analysis stands or falls with the quality of the reference material.

- For dual analyses: (C and N)

We bought 2kg of flour (the cheapest flour available :-) and had it
calibrated  by iso-analytical. We have devided the flour into small
portions of about 200 grams for storage. The people at iso-
analytical say that the flour can be kept for a long time in this way.
So, now we have about 2kg of flour, with known atom% 13C,
atom%15N, total C and total N. This flour will be used for most
analyses we do in our lab.

When we have to analyse samples that have a totally different C/N
ratio, we will use our IAEA-references. By mixing sucrose and
ammoniumsulfate we can achieve every C to N ratio we desire.

- For single analyses: (C or N, seperately)

For this we have bought sucrose and ammoniumsulfate in 'larger'
quantities and have calibrated them ourselves, against our IAEA-
reference materials. These reference materials will be checked on
a regular base.

To conclude I can say that we're also experimenting with: citric
acid, leucine and acetanilide.

If there are any questions, feel free to ask them. It's easier (and
faster) to achieve good results when people cooperate!
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Peter Vervloedt
Ghent University
Laboratory of Applied Physical Chemistry
Coupure Links, 653
9000 Gent
tel.: +32 9 264 60 00
fax.: +32 9 264 62 30
e-mail: [log in to unmask]
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