Abstract
SUMMARY The conversion of glyceryl esters to derivatives suitable for gas-liquid chromatography was accomplished by hydrogenolysis with lithium aluminum hydride followed by direct acetylation of lithium aluminum alcoholates with acetic anhydride. Fatty acids and glycerol were converted quantitatively to their corresponding acetate esters by this procedure. Gas-liquid and thin-layer chromatographic procedures were used to demonstrate quantitative acetylation. Acetate esters of fatty alcohols and glycerol were recovered together and analyzed by gas-liquid chromatography to give a simultaneous estimation of fatty acid composition and the ester-glycerol ratio. Quantitative results were obtained for mono-, di-, and triglycerides. The quantitative estimation of glycerol and fatty acids in glycerides requires either acid or alkaline hydrolysis and an extraction process to separate the aqueous glycerol and nonpolar fatty acid phases. Glycerol in the aqueous phase is then assayed by paper chromatography (I), periodic acid oxidation (24), an enzymatic procedure employing glycerophosphate dehydrogenase (5) , or a microbiological determination (6). Fatty acids in the nonaqueous phase are characterized by a number of procedures that generally require the preliminary conversion of fatty acids to their methyl esters. These procedures for the estimation of glycerol and fatty acid composition have several limitations (7). Hydrolysis may be incomplete or the glycerol partially decomposed. Periodic acid oxidation is relatively nonspecific, and the purification of glycerol is often necessary in quantitative studies. Fatty acids in the nonaqueous phase usually require concentration or isolation before esterification. An
Highlights
Glycerol in the aqueous phase is assayed by paper chromatography (I), periodic acid oxidation ( 2 4 ), a n enzymatic procedure employing glycerophosphate dehydrogenase [5], or a microbiological determination
Fatty acids in the nonaqueous phase are characterized by a number of procedures that generally require the preliminary conversion of fatty acids to their methyl esters
Periodic acid oxidation is relatively nonspecific, and the purification of glycerol is often necessary in quantitative studies
Summary
The fatty acid content of glyceride and fatty acid methyl ester preparations showed over 99% purity on gas-liquid chromatographic analysis. 200 mg, was dissolved in 30 ml of dry ether. The residue was allowed to settle and the lithium aluminum hydride solution was transferred by alcohol acetates, 0.90; diglycerides, 0.80; fatty alcohols, 0.55; and monoglycerides, 0.18. Twenty milliliters of acetic anhydride was added, dropwise a t first This mixture was heated to evaporate ether and refluxed for 2 to 4 hours a t the boiling point of acetic anhydride. The contents of the flask were extracted with ether and the ether was washed with water This ether solution was filtered through anhydrous sodium sulfate and reduced in volume for gas-liquid chromatography. Samples varying in size from 5 mg to 1 g can be used together with a propor-
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