Dear Nicolas and others,

My reaction on your message in fact was not meant in any personal way. I
just recognized this 'scale' problem when reading your text. I realize quite
well you did not mean to start this discussion, and your query was not on
this matter - about that Roy Krouse gave you a nice answer I think.
The problem of using diferent techniques and different scales, and therefore
eventually different values, is not new. But it may give serious bias of
interpretation of results - that simply was the point I wanted to bring
forward.
You mentioned yet another topic on this scale problem: the homogenity of
sample material. This is a serious problem, indeed. Just think about the
S-CDT inhomogenity, already history.... This increasingly will be a matter
of discussion, the problem of standards we hear about regularly on this
list. I agree with you on this.

I did not really want to dispute what you wrote. For some time already I
have my worries about this topic of measuring in different ways and getting
to different interpretation. Clearly not the case in your meassage... You
message just triggered my reaction! It is all about what values are we
looking at, what do they represent and how do we interprete them.
You did not release my worry, but actually increased it with adding your own
'worries' on the reference materials. But fair enough, completely correct.
Sorry if you felt 'attacked' - that was not my aim. I hoped for some
reractions on this (maybe still to come) - besides some to me personal
directed reactions....
Or do we deal with the measuring only on this list?

Best wishes,
Pier.


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***************
Dr. Pier A. de Groot
European Commission
Joint Research Centre
Institute for Reference Materials and Measurements (IRMM)
Retieseweg
2440 Geel
Belgium
Tel. +32 (0)14 571 628
Fax +32 (0)14 584 273
e-mail: [log in to unmask]

Visit my WEB-site about my "Handbook of Stable Isotope Analytical
Techniques" at:
http://www.geocities.com/padegroot/index.html
last update: 9 July, 2001.
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-----Original Message-----
From:   Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Nicolas Patris
Sent:   17 August 2001 02:41
To:     [log in to unmask]
Subject:        Re: d34S of native S by EA-IRMS

Dear Pier,

Pier De Groot wrote:
>
> Dear Nicolas and others,
>
> I basically agree with your reasoning. Probably the small amount of S
> used is oxidized before it can evaporate and swept out by carrier gas
> and be deposited as native sulfur in cooler parts of the device (if
> not, you have a serious problem).
>
> But one factor worries me ...
> You state that, if taking smaller portions homogenity is a problem.

Nope. I don't.

> [...] So, considering the above reasoning, I do not agree with
> Nicolas' statement that smaller sample create 'problems'

Neither do I.
BTW, this was not my statement.

What I wrote is that homogeneity of smaller samples is a *concern*, i.e.
that one might want to bear in mind the potential grain to grain
variability which can be accessed at these levels.
You can see it as a -limited- problem (how representative are my data
points), or as a nice way to go into further details (as you said,
extended isotope range and such), depending on your interest, or maybe
on how anxious you are?
Be (re)assured I have nothing against the progress of science, and I'm
glad new techniques allow more and more refined types of analysis ;)
I, for instance, really look forward to the coming day we can achieve
reliable isotope measurements on grain by grain or intra-grain aerosol
studies...

One real limitation though might be the homogeneity of solid reference
materials which is not guaranteed at very low levels (this at least
concerns solid material techniques, such as continuous flow EA-IRMS).
I hope this will help relieve at least some of your worries...
Cheers
Nicolas
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