Chromatography Forum

Hello,

I'm working with a mixture of fatty acid methyl esters, and I'm having trouble getting better resolution between the C18 - C20 compounds. How can I increase my separation?

p.s. I'm a newbie at the GC.

If you are trying to separate saturated FAMEs then lengthening the column you are using and optimizing the carrier flow rate will help.

Using a thinner film thickness will generally improve the number of theoretical plates as well as a more narrow bore capillary column if you are using capillary columns.

Reducing the oven temperature can improve separation but can be taken too far. Usually temperatures of 180°C to 200°C are suggested for the analytes in question.

If you are trying to separate unsaturated FAMEs then selecting a more polar column or a column designed for FAME separation such as Supelco's Omegawax would be the best suggestion I can offer you.

Perhaps a call to Supelco's technical service and getting some free advice might be a good direction to start.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823
rodney.george@sial.com

800-359-3041 technical service
techservice@sial.com

Thanks.

I'm using a JW DB-23, 60m, 0.25 ID, .25 film. THis column is supposed to be good for FAMEs. Would the supelco omegawax be superior to this?

Nabearup,

If you tell me the separation you are trying to achieve I might be able to give you a good answer.

There are more polar columns than the DB-23 and there are less polar columns.

Do you know which FAMEs you are trying to separate?

best wishes,

Rod

I get separation, but the peaks are so close to each other. this makes it difficult to determine which peaks are for the trans isomers for linolenic (c18:3), oleic (c18:1) and linoleic (c18:2). Thanks

Nicole

http://www.sigmaaldrich.com/Brands/Supe ... study.html

http://www.sigmaaldrich.com/Area_of_Int ... p2560.html

Here are some web documents that may be helpful for you.

technical service at Supelco could have given you additional assistance.

Feel free to contact them. It is a FREE service.

best wishes,

Rod

I think Rod works for Supelco, and he's absolutely right here. Most chromatography companies have good telephone technical help. We typically use a Supelco SP-2330 phase with packed for routine FAMEs (such as from bar soaps), and an SP-2330 capillary when we need to resolve methyl elaidate and methyl oleate. We've also used longer (up to 60m) Supelco SP-2340 capillaries.

Thanks for the suggestions.

Well, just so happened that a customer requested this assay today, so I looked it up.
Last time we used Supelco #24109 SP-2380 capillary.