Chromatography Forum

Hi,
I need to analyze fatty acid composition of commercial magnesium stearate (mainly mix of stearic and palmitic acid) but I've no experience with derivatization.
Please can you help me with all informations I need? Is it a difficult sample preparation?
Also link to technical paper will be appreciate.

thanks a lot.

You basically have hard-water soap. See AOCS Methods Ce 1-62 and Ce 2-66, Official Methods and Recommended Practices of the American Oil Chemists Society and L.D. Metcalfe and A.A. Schmitz, "The Rapid Preparation of Fatty Acid Esters for Gas Chromatographic Analysis", Analytical Chemistry, 33 (1961), pp. 363-364.

Realistically, since you don't contain any unsaturates, anything from a DB-1 type column to SP-2330 type (best for traditional soaps containing unsaturates) can be used to separate as the methyl esters. Cautiously add 140 ml sulfuric acid to 860 ml methanol and mix (or use 12% boron trifluoride in methanol instead). Take like 2 grams sample and 15 ml sulfuric acid reagent above in a 100 ml VF, heat/stir on steam bath 10 minutes, cool, add 15 ml petroleum ether or hexane and swirl, add saturated NaCl, stopper and mix, allow to separate. Inject upper organic layer into GC.