We want to monitor the stability of omega-3 fatty acids by GCMS, specifically DHA - docosahexaenoic acid, and EPA - eicosapentaenoic acid.

I have two questions:

1) Methyl esters or Free fatty acids? What does everyone reccomend? What column?

2) Is it possible to get pure DHA and EPA? We have sources of fish oil and such, but it would obviously be simpler if we could work with "pure" materials.

Thanks,

Mike

I work for soap company. We make fatty acid methyl esters, and use polar columns such as SP-2330 (Supelco) and Rtx-2330 (Restek) but have used PEG columns (and DEGS in the olden days). We've had good success getting pure fatty acids, esters, and monoglycerides from Nu Chek Prep, in the midwest.

OK, I'm doing methyl esters. Now, I am trying to follow an AOCS method for Fatty Acids. I've never done this before, so please bear with me.

The method calls for derivitization with BF3/MeOH. By the time all of the reagents are added during the derivitization step, I have a total volume of 9.5mls. I can't find reaction vials larger than 5mls. Will thie reaction generate a lot of heat/pressure, or can I do it in a 15ml screw cap tube centrifuge tube?

Any suggestions? I'm just having a hard time getting started on this.

"I'm trying to think but nothing happens."

Thanks,

Mike

You could use 20 ml scintillation vials or 40 ml I-Chem vials. We normally use 100 ml volumetric flasks, 20 ml BF3-methanol, heat on steam bath 5 minutes (no stopper), cool, add 20 ml petroleum ether & swirl, add saturated NaCl, stopper and mix, inject top layer.

i am in a chem college class and I need to know what the process of spotting a plate is? and how to calculate the Rf for certain spots

help!

I have used 15mL culture tubes with teflon lined screw caps for years. I heat the tubes entirely in a 100°C oven or heating block. I usually place 10-25mg of free acid with 1mL of hexane or CH2Cl2 and 1mL of 14% BF3 in Methanol.

Heat only 6-8 minutes, cool and add concentrated saturated NaCl aqueous solution to extract. Hexane layer is on top (preferred) or methylene chloride layer is on bottom.

Heating over 8 minutes will degrade the polyunsaturated fatty acids. Over 10 minutes and the analysis is unreliable. Check by TLC for completion of reaction and for any byproducts.

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

Anonymous chem student

Use 1 or 5 µL capillary glass tube for spotting a solution of analytes.

Usually solution is at a conc of 20 to 100mg per mL. Spot different dilutions of the first solution to evaluate impurities' concentration.

Make all spots at same distance down from the top of the plate but along the horizonal width of the plate starting near the center if possible.

Calculate the relative distance of the migration of the 'spot' to the distance the solvent travels up the plate. This is called the 'retardation' factor. If a spot travels 2cm and the solvent travels 10cm, the Rf is 0.20

Good luck

I use 16 x 100 mm test tubes capped with standard sized marbles in a heating block. The solutions reflux but do not evaporate.