Chromatography Forum

Hi!, first of all, sorry for my english, i do my best but i am French .

I would like to identify chain of fatty acid of vegetable oils like sweet almond oil or sunflower seed oil.
i have a norm ( EN 12966-3) which explain me how to convert the fatty acid in the corresponding O-methyl ether derivatives using solutions of TBME and TMSH.
now, my question :
In my lab i have only one column : DB-Wax 20 m on a GC7890B Agilent.
i would like to know this PEG column si ok to do this analyse ?
thanks a lot for yours answers.

I have used 30m wax columns for FAME analysis before and achieved good results - this was in line with conditions in European Pharmacopoiea general chapter 2.4.22.

As far as I can recall, the FAME peaks were nice and sharp so you should have no problems, unless you are looking at very long chain fatty acids that require elution temperatures above the max temp of your wax column.

I agree with AaronAIT. I believe that you will have success with your column. I use 30 m x 0.53 mm x 1.0 µm wax columns for my FFA analysis. I can get C22 FAMES to come out at 240 °C (below the temperature limit of my columns). If you're looking for heavier than that, you might have trouble.

Thanks a lot for yours answers.

since we have not much credits in my lab I did not wish to make a mistake.

i'm more relieved now.
thanks

I use the mild methanolysis protocol from the journal of lipid research. It works pretty well and I can make the reagents out of common lab reagents.
http://www.jlr.org/content/51/3/635.full

I don't do FAMES too often and when I do it is usually for identification purposes so I just make overlays of the common oils.

I assayed fatty acid methyl esters by GC for over 40 years. Thousands of times the samples were fatty acids or soaps, but about 500 times the samples were triglycerides like the vegetable oils in question.

My prep was to take about 1 gram sample and heat 15 minutes with about 10 ml KOH or NaOH made up in methanol at about 0.5N; use a flask or something with a condenser (this step was omitted if sample was laready fatty acid or soap). Then I added 15 ml of 10% H2SO4 made up in methanol (or 10% BF3 in methanol), heated an additional 5 minutes. Then I cooled it, added some hexane and swirled, added saturated NaCl, shook, and took some of the hexane layer into an autosampler vial for GC assay.

I started using packed columns, DEGS was common back then, but sensitive to moisture and heat degradation, so we switched to more-stable SP-2330. Once we went to capillary GC in the late 1970s, I used capillary SP-2330 by several column makers, thought it was more stable than PEG columns like DB-Wax, same elution order.

Bonjour ikiikitapong

First, please don't apologise - your English is better than our French

In addition to the above answers - yes your column would be fine for the analysis of the fatty acid methyl esters derivative from the fatty acids produced from hydrolysis of the oils.

I have a slight concern over your using solutions of TBME and TMSH.

Just look at the the other suggestions posted previously and this article
http://lipidlibrary.aocs.org/Analysis/c ... mber=40374

If it is of any help I have tables of the chain length distributions of the fatty acids of common vegetable oils that I can pass on to you if you wish

à votre santé

Ralph

Hello,

In the past, I analyzed FAMEs from vegetable oils using transesterification process of converting vegetable oils to FAMEs with 1 wt% solution of sodium methoxide in methanol with some heat. Then, partition the transesterified oil between water and hexane. The hexane containing FAMEs were analyzed in an Agilent HP-5 column or DB-225 column.

I will reed the very interesting links you posted.( it will take me a while.)

i will repost here my first result.

thanks a lot to all of you!

A bientot !

ikiikitapong, probably this column will works fine for your sample.
One of the most widespread method for FAME analysis (EN 14103) recommends a DB-Wax column with specification of 30m x 0,32mm x 0,25 um.

Leonardo.

The USP also lists the acceptable range for fatty acid compositions of various vegetable oils like sunflower, soybean, and corn oil. See the applicable monographs.