Determination of glycerol by gas chromatography using meso-erythritol as internal standard

A simple chemical method for the determination of the glycerol moiety of triacylglycerols in lipids is described. The internal standard meso-erythritol is added and the mixture saponified in 0.5 M sodium hydroxide in methanol under reflux for 10 min. After cooling, the mixture is acidified with 2 M hydrochloric acid and the fatty acids extracted with hexane. The aqueous phase is then passed over a mixed cation–anion exchange resin, the eluate concentrated on the rotary evaporator below 40 °C, dried overnight in a desiccator and glycerol plus meso-erythritol converted into their respective trimethylsilyl ethers by treatment with chlorotrimethylsilane and hexamethyldisilazane in pyridine. The silyl ethers are separated by capillary gas chromatography yielding the glycerol content of the lipid. As phospholipids yield mainly (>95%) glycerophosphate under our conditions of hydrolysis, which is subsequently removed by the mixed ion-exchange resin, the glycerol content is a measure of the triacylglycerol content of the original sample. A suitable correction for the presence of phospholipids can be applied by determining the phosphorus content of the lipids. In the majority of cases encountered this correction was negligible. The method is suitable for all compounds releasing glycerol on saponification, but it is especially useful for determining small amounts of triacylglycerols in an excess of wax esters. Examples of triacylglycerol determinations in the lipids of a number of South Atlantic fish species are presented.