Abstract
(1) Submicro quantities of methyl esters for gas-liquid chromatography (GLC) can be prepared quantitively and rapidly by alkali-catalyzed transesterification with sodium methylate. Under the conditions described, sodium methylate splits only the ester and not the acid-amide linkage. This was demonstrated on ester cerebrosides, a group of glycolipids. (2) A general method (Method A) is described for all lipids with ester bound fatty acids (glycerides, glycerophosphatides, cholesterol esters, waxes and ester cerebrosides). This method is recommended especially for the transesterification of cholesterol esters. The lipids are dissolved in a small quantity of benzene. After the addition of 0.5 N sodium methylate the mixture is heated to boiling point. Within two minutes the transesterification is complete. Glycerides and glycerophosphatides react already at room temperature within the same time. The reaction mixture is neutralized, the solvent evaporated, and the methyl esters in the residue are extracted for GLC analysis. (3) With the second method (Method B) glycerides and glycerophosphatides can be directly transesterified within 5 min after their application on silicic acid plates by spraying with 2 N sodium methylate. The method is very convenient for the GLC analysis of lipids separated by thin-layer chromatography. After trans-esterification, the methyl esters are eluted with ether into a special tube, which is suitable for the collection of very small quantities. The silicic acid plate can also be used for the parallel preparation of many samples. (4) Because of the interference of fatty acid methyl esters and long-chain alcohols in GLC analysis, the alcohols were separated from the methyl esters by preparative thin-layer chromatography after the transesterification of waxes.
Published Version
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