Edible Oils analysis
Posted: Wed Apr 05, 2006 1:23 pm
by msimone
I am currently involved in analysis of some edible vegetable oils. Ideally I would like to be able to look at the triglycerides, and free fatty acids in the same run. I am interested in free fatty acids as a degradation product of the oil, so I can't do FAMEs by GC.
Right now I can get pretty decent looking chromatograms for the triglycerides using a C8 column and a ACN/Ethanol/Water gradient. However I do not seem to be retaining/resolving the FFAs well. If I run a similar gradient using a C18 column, I resolve the FFAs better, but I have some co-elution of the triglycerides.
Any thoughts, any Oil Analysis experts out there?
Thanks,
Mike
Posted: Wed Apr 05, 2006 2:45 pm
by Bryan Evans
Posted: Wed Apr 05, 2006 8:06 pm
by Bruce Hamilton
I can't help too much with the HPLC method, but have used two 250mm C18 columns in series to resolve Triglycerides from FFA and sterols, but it only worked for oils with C16 and C18 fatty acids, too much overlap for others, but there may be better columns available now.
Many standard methods for edible oils exist and the American Oil Chemists Society website may be able to offer suggestions or contacts.
I've looked at Free Fatty Acids in triglyceride oils using GC, by dissolution in iso-octane and bubbling diazomethane through to derivatise the FFA, and then inject into a GC column - can get FFA and TAGs ( triacylglycerides ). With acetylation ( pyridine/acetic anhydride ), you can also get MAGs, DAGs, but I've not tried FFA, MAG, DAG, TAG on a single sample run, usually usedtwo runs, FFA and TAG, and sterols, MAG, DAG, TAG.
I know DAM isn't sexy these days ( carcinogenic or similar, with toxic precusors ), but the derivatisation only takes a minute, and there are some simple DAM generators available. So if you don't have much luck with HPLC, you could revisit GC. There are methods out there for GC.
Bruce Hamilton
Posted: Wed Apr 05, 2006 10:28 pm
by Fabiano
There is a Czech group with a paper in which he resolves FFA, mono, di e triglycerides in the same run with APCI as detector.
Really nice paper, unfortunatelly I don' have it anymore.
In the lab I worked, people use 1 or 2(better) 250mm C18 columns.
They had nice cromatograms, I recomend this mobile phase:
http://pubs.acs.org/cgi-bin/abstract.cg ... 1667d.html
If you don´t have all standards for triglycerides take a look for some papers about ECL and ECN, like kovats index for lipids...
Fabiano