VITAMIN-A QUANTIFICATION IN FLUID DAIRY-PRODUCTS - RAPID METHOD FOR VITAMIN-A EXTRACTION FOR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A rapid method has been developed to extract retinol from saponified milk and from half and half samples for vitamin A determination by reverse-phase HPLC. Saponification, extraction, and washing steps were conducted in a single test tube. An aliquot of the organic extraction phase was evaporated and redissolved in methanol for HPLC injection. Four different solvent systems, diethyl ether, petroleum ether, hexane, and diethyl ether:petroleum ether (1:1), were evaluated for their retinol extraction efficiency from the digest. A method that uses several extractions and washing steps with separatory funnels was used as a reference saponification and extraction method. Diethyl ether:petroleum ether (1:1) gave the highest retinol extraction efficiencies, between 101.5 and 103.6%, when compared with the reference procedure for milk, half and half, and a retinol acetate standard. The lowest results were obtained when using hexane. In studies of the recovery of added, all-trans retinol from augmented samples using the rapid method diethyl ether:petroleum ether gave recoveries generally greater than 98%. This method is rapid and benefits from the use of mixing vortex for maximum extraction and centrifugation to break the emulsion.