Dear Ian (and other users of medium polar / polar columns),
I'm using stationary phases of medium polarity to high polarity on a
regular basis for amino acid (NAP) and FAME work. I'm especially
fond of my BPX70s, which have served me well for a number of
years now (4, I think; years, that is).
> A quick query to solicit opinions on the suitability or otherwise of highly polar stationary phase GC columns for irm-GCMS of fatty acid methyl esters (FAMEs). We have previously been using SGE's BPX-70 column which gives excellent resolution of polyunsaturated acids. However, even without
using this column in the oxygen-rich environment of a irm-GCMS it appears to degrade remarkably quickly. As an example, a new column installed briefly around 6 months ago for a few analyses appears to have degraded to the point of very poor performance while sat sealed on a shelf in the mean
time. Anyone got experience on the longevity of other similar columns - at $400 a shot they're too expensive to use this way.
>
The only two problems with these stationary phases (polyglycol
based ones more than cyanopropyl ones) are their oxygen- and
light-sensitivity. Of course, there is always the chance you get a
column from a bad batch as making good polar columns is
notoriously more difficult than making good apolar columns.
With such columns one should use He of the highest purity
(shouldn't one always? especially in IRMS) such as 5.5 or 6.0 (=
99.9995% and 99.9999%, respectively). I go for the overkill in terms
of carrier gas purity and use a Supelco thermo-chemical gas
purifier in conjunction with 5.5 He to ensure my carrier gas is O2
and H2O free. The nice thing about O2-free He is that you can
ramp you polar column up to 360 C without any adverse effects
(provided the column has been coated properly; so far I was lucky
with mine). It's really the O2 that kills the column, not the
temperature. Ideally, one would use H2 as carrier gas but for
obvious reasons that is not an option for GC/C-IRMS.
The other thing is storage. Uninstall the column at the interface end
first with He still gently flowing through the column. Seal end with
septum (you can even flame seal it with one of these nifty pocket
blue torches one often sees on cookery programmes) then
disconnect at injector end and seal. I then wrap the column in
baking foil (house-hold tin foil) before I put it in the cupboard.
Sounds hilarious, I know, but it works.
Hope this helps.
Best regards,
Wolfram
***********************************
Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow
University of Dundee, School of Life Sciences,
OMS, Small's Wynd, DUNDEE DD1 4HN, United Kingdom
Tel.: +44-(0)1382-34/5124, /4574, /4968
Fax: +44-(0)1382-34/5514
e-mail: [log in to unmask]
URL1: http://www.dundee.ac.uk/biocentre/SLSBDIV6wma.htm
URL2: http://www.dundee.ac.uk/anatphys/wma/meieraug.htm
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