Print

Print


Hi Chris,


All these columns are based on the same stationary phase, a polymethylsiloxane with 5% substitution of phenyl for methyl groups (i.e. 5% phenyl, 95% methyl siloxane); its generic name is SE52. The difference the column manufacturers claim relate to their own "secret" way of cross-linking the phase once coated on to the glass wall for increased stability (low column bleed at high temperatures).

My advice to you if you choose to accept it is NOT to use trifluoroacetylation to derivatize AAs. I know this is one of the best derivatization methods for AAs to obtain a sharp, well resolved GC chromatograms BUT it is also a sure-fire way to exhaust your oxidation reactor very fast and irreversibly (the formation of copper and  nickel fluorides makes a re-oxidation impossible).

Ref.: W Meier-Augenstein: “GC and IRMS Technology for 13C and 15N Analysis of Organic Compounds and Related Gases”, in Handbook of Stable Isotope Analytical Techniques by Pier de Groot [ed.], Elsevier Science Publishers B.V., Amsterdam, (2004), Vol. I, part 1, chapter 8, 153-174; ISBN 0-444-51114-8.

The specific information on this subject can be found on page 162.

I am not telling you what to do but I am suggesting you ask yourself the following two questions.

1. Do you have the time and (financial) resources to discard and replace oxidation reactor tubes every other day (the exact frequency of course depends on number of samples run and AA concentration/s)?

2. Are you prepared to trust the resulting d13C values considering TFA derivatized AAs are not combusted quantitatively (more like 50% of theoretical CO2 yield) and, hence, the presumption of isotopic fractionation free sample conversion is no longer valid?


Best,

Wolfram


________________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Chris Chambers [[log in to unmask]]
Sent: 25 January 2008 19:52
To: [log in to unmask]
Subject: [ISOGEOCHEM] GC/C-IRMS

Has anyone tried running trifluoroacetylated amino acids on an Rtx-5SilMS
(Restek) or DB-5MS (Agilent) column?  I know they have very similar
stationary phases to the DB-5 type columns that appear in the literature for
this method, I was just wondering if anyone knows if they are different
enough to affect peak resolution in some or all amino acids.

I appreciate any input...

Chris Chambers
School of Biological Science
Washington State University
Pullman, WA  99164
[log in to unmask]