Dear Frank,

This is going to be a fairly radical suggestion but should narrowing
down the source of your problem.

You can try to run procedure duplicates using methods other than
Indiana Zinc such as equilibration using Pt-on-alumina catalyst
[1] or reduction employing Tanweer's Mn protocol [2]. And then there
is always the acetylene method.

This should at least tell you if the degree of uncertainty is caused
by your current sample preparation. Another way of going about would
be to prepare sample duplicates sticking to your current routine and
have the samples double-checked on another IRMS.


All the best,
                         Wolfram


[1] Scrimgeour, C.M. et al.; J. Biol. Mass Spectrom., 22, 383-387
(1993)

[2] Tanweer, A., amd Han. L.-F., Isotopes Environ. Health Stud., 32,
97-103 (1996)




*****************************************************
Dr. W. Meier-Augenstein
Lecturer/Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4968
      +44-(0)468 -314563
Fax:  +44-(0)1382-34/5514

e-mail: [log in to unmask]

URL: http://www.dundee.ac.uk/AnatPhys/wma/wolfram.htm
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