Dear Stephen,

Thank you very much for your communication which did a lot to restore
my faith in myself (and my fellow scientists).

> Mike Engel (at Oklahoma) and I have successfully run 13C and
> 15N on
> individual amino acids (and separated their stereoisomers)
> using TFAA/Isopropyl esters, on a Chirasil-Val column
> (Alltech). Arginine survives the derivatization and comes
> out quite late. TFAA/IP amino acids can be resolved on
> other polar phases, but not as stereoisomers. ASN and GLN
> do not survive the esterification, and come out with the
> ASP and GLU peaks. TMS derivatives do not destroy the GLN
> and ASN. When I run TFA amino acids, the furnace (I have an
> OPTIMA and ISOPRIME with respective interfaces) survive for
> a while , and then go catastrophically (they seal off, and
> my flow drops to zero.

Which confirms my own observations. Some time ago I did some
development work on enantioselective stationary phases for GC
(basically cyclodextrin derivatives in OV-1701) and found that TFA/M
and TFA/iP give the best chiral separation for amino acids. I always
wanted to combine this technique with IRMS as I suspected
stereochemical reasons behind certain inherited metabolic disorders.

However, the adverse reactions of F with the combustion catalyst
thwarted my attempts in this direction. Having seen the negative
impact on conversion rates (reduction of CO2 formation by 50%) I
abandoned the idea for the time being as I didn't have any
confidence in the d13C and d15N values thus generated. I must admit I
never took the time to compare d13C and d15N from NAP with TFA/iP
from of-the-shelf amino acids to see how serious the problem was.
Wouldn't that make a nice little study?

I was hoping that the new catalyst I'm experimenting with at the
moment would solve the problem as it achieves complete conversion
into CO2 and N2 in one step at 370 C. However, no such luck. This
particular catalyst composite is even more sensitive to F albeit for
different chemical reasons. So, back to the drawing board.


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

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