Dear Hector,

>
>         I like to comment that two years ago we tried Mn as reducing agent,
> and our experience was bad.  Despite we closely reproduced  the conditions
> listed by Tanweer et al., we obtained important and no reproducible shifts
> in delta values.  In addition finest particles of Mn entered wherever in the
> inlet system of our delta-S mass spectrometer.  All  this led us to abandon
> the technique and continue buying Zn in Indiana.
>

I am sorry to learn about the problem you experienced but I'm sure
you will appreciate that it is difficult for me to comment. All I can
say is that I never encountered problems such as mentioned by
you.

The truth to be told, ever since I moved to Dundee I had no
opportunity to use the Mn method (lack if equipment). Here, the lab
is set up for the acetylene method, which I understand is a similar
bone of contention between various groups. Again, in our hands the
methods works just fine, with optimum results for sample sizes of
2 to 3 microlitres of urine or water.

The beauty of this method is that it takes less time and run at
room temperature (even in the Scottish climate).

We routinely run a standard calibration curve with each sample
batch using a serial dilution of 99.9% D2O.

There is no significant sample size dependence but the best
results are obtained from samples of 2 ul; S.D. is typically  0.0004
atom%, and coefficient of variation is typically 0.018%. For 4 ul
samples S.D. is 0.0006 atom% and cv is 0.029%.

Whether this is down to our sample handling or to our particular
batch of calcium carbide, I wouldn't care to speculate. The moment
we run out of our current stock of calcium carbide we'll probably
find out.


Best regards,

                        Wolfram



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Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
OMS, DUNDEE  DD1 4HN, United Kingdom

Tel. (B): +44-(0)1382-34/5124 or /4574
Fax  (B): +44-(0)1382-34/5514

e-mail (B): [log in to unmask]

URL: http://www.dundee.ac.uk/anatphys/wma/meieraug.htm
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