Fatty acids: analysis techniques?

On Thu, 17 Jul 2003 11:14:19 GMT, [Only registered users see links. ] (MC) wrote:


I think you may be pushing shit uphill to capture C1 - C18 with a
single analysis - unless you have a specific system that allows you to
perform the analysis without solvents that will also provide peaks
in the "volatile fatty acid" region ( C2 - C7, but may also include
such species as lactic acid ). Formic acid is tricky, most methods
usually start at acetic.

I assume that you only want to capture the Free Fatty Acids, not all
the lipid fatty acids. If you are going to submit the information to a
regulator, they may already define which techniques should be used. If
you want the total fatty acids, some form of interesterification or
hydrolysis will be necessary.

Standard GC methods for fatty acids in foods etc, usually can cope
with C4-C30 fatty acids, but capturing and quantifying the "volatile
fatty acids " ( C2 - C 7 ) could be a little messy, as those volatiles
may co-elute with other material, so you may need a separate method.

You may want to consider doing the volatile fatty acids by ion
chromatography, which would also allow you to measure formic acid, and
using the standard solvent-based GC methods used in food, water, and
wastes for the remainder.

You may also find that sewage sludge has fatty acids that are longer
than C18, depending on how sensitive you want to be, and your reason
for needing the information.

There are plenty of methods for Free Fatty Acids, Volatile Fatty Acids
( using GC, IC, and HPLC) and you need to decide what methods you can
do, and what information you want. If you narrow your search down
using the specific type of assay ( FFA, VFA etc ) and techniques you
have available, you should find plenty of detailed methods on the WWW.

You may find it faster and cheaper to send the samples to a laboratory
already performing the analysis.

Bruce Hamilton

[Only registered users see links. ] (Bruce Hamilton) wrote in message news:<[Only registered users see links. ].nz>.. .

In 1985-86 sometime, as a grad student in Brookings,
South Dakota, I had the opportunity to help out an
agricultural guy (scientist, professor...whatever)
with a GC analysis of silage samples (wet samples
provided to me) using a Hewlett Packard GC...I forget
the product number (3xxx), but the oven was perhaps
4-5 feet tall, and the small-bore glass column was u-shaped
and 3-4 feet overall. The trick was to treat the
packing (may've been OV-17) with phosphoric acid.
He was looking at short-chain FA's (IIRC) and was
so pleased with the results he was getting, I got
an invite down to his office where he shared some
graphs with me (change in acids with time). Newer
multi-meter glass capillary columns might be available
for the entire range of acids...would have to nose
around for websites of providers and ask for tech
assistance.

[snip...]


Mark (Oh...for the days of innocence, where all there
was to argue about was, who washes the glassware :-)

"Mark Tarka" <[Only registered users see links. ]> wrote in message
news:6b70c71c.0307190656.59aac50b@posting.google.c om...
news:<[Only registered users see links. ].nz>.. .
in
to


Things have come on a bit since then!

Andy