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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Steville on July 18, 2021, 07:18:15 PM

Title: derivitisation and LC/MS of vegetable oils
Post by: Steville on July 18, 2021, 07:18:15 PM: Hi all,

I'm a polymer chemist, currently looking to characterize various natural oils (eg coconut, avocado, hazelnut etc).

As you all may know, these oils are composed of triglycerides with various fatty acid chains. I need to simply know the % composition of each fatty acid, so I need to break down the triglycerides to their component fatty acids (assuming esterification), separate somehow (assuming LC) then identify/quantify (assuming MS of some sort).

Does anyone have a standard method for this? I see papers galore for "edible oils" and LC MS for this type of sample, but no simple method (as I'm sure it's a pretty standard kind of process and not really worthy of a paper).

Any help would be hugely appreciated.

Stephen
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: Babcock_Hall on July 19, 2021, 08:35:33 AM: You might also try searching on biodiesel. I bet quite a bit will come up. Fatty acid methyl esters are usually abbreviated as FAMEs.
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: shchavel on July 19, 2021, 12:57:44 PM: I know that there are some Gas chromatography methods, that used in pharmaceutical field to solve the similar problems.
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: Babcock_Hall on July 19, 2021, 04:32:12 PM: Most likely you would perform a transesterification to the methyl ester, or perhaps to another ester.
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: Babcock_Hall on July 20, 2021, 03:23:47 PM: https://www.sigmaaldrich.com/US/en/product/supelco/me101kt?gclid=Cj0KCQjw6NmHBhD2ARIsAI3hrM3vLwNst5xCsps13jd-Sa0T5AbCilgwnezZQF8UprZZWdx0eo5NrMYaAgT_EALw_wcB
https://www.restek.com/en/technical-literature-library/articles/high-resolution-GC-analyses-of-fatty-acid-methyl-esters-fames/

I would be tempted to use GC-based methods, given how well known these methods are, unless there is an advantage to LC-based methods for some reason. .Standard FAME mixtures are available commercially.
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: Steville on July 21, 2021, 02:50:57 PM: Hi all,

Thanks for the excellent responses!

I'll try the GC route and see if I can get a standard sample with a variety of esters.
I'll keep you all posted and tell you if I overload the column!

Stephen
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: wildfyr on July 27, 2021, 08:05:48 PM: Definitely a job for GCMS.

One great trick is that if you dissolve all your crap in MeOH and add a tiny amount of sulfuric acid and let it stir, everything will come out methyl ester. Its dead easy.
Title: Re: derivitisation and LC/MS of vegetable oils
Post by: ablake on August 02, 2021, 03:33:11 PM: We use butyl esterification for medium chain fatty acids on GCMS. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0224454
Same method, just leave out the silylation step. Just make sure to include a good post run oven temperature ramp to purge out everything and prevent sample carryover.

Also, I would suggest getting a deuterated internal standard of a short, medium, and long chain FA at the minimum. Don't get standards that are already esterified because then it wont account for if the esterification step went to completion on your unknowns/samples.