Variable recoveries of fatty acids following the separation of lipids on commercial silica gel TLC plates Selective loss of unsaturated fatty acids on certain brands of plates

Since we recently noticed poor recoveries of unsaturated fatty acids (UFA) when the parent lipids were first separated on TLC plates, we investigated the source of this error by examining several variables, including the brand of TLC plate, nature of the lipid, and conditions of methylation. Of the five commercial brands of plates used, two (Baker and Whatman) showed loss of UFA, and three (Alltech Hardlayer, Alltech Softlayer, and Merck) did not. This loss occurred in both neutral and phospholipids, did not affect saturated acids, and was independent of the methylation reagent used. No loss occurred, however, if the lipids were eluted from the silica gel before methylation, indicating that the loss is due to oxidation of UFA in presence of certain brands of silica gel. These results show that some brands of TLC plates may be unsuitable for lipid analysis, if the aim is to determine the fatty acid composition by GC using direct methylation.