Determination of vitamin A and vitamin E esters in infant formulae and fortified milk powders by HPLC: Use of internal standardisation.

An HPLC method is described using normal phase conditions with an unbonded silica column to determine concentrations of supplementary vitamin A and vitamin E esters and β-carotene in infant formulae. The method utilises selective dual-channel fluoresence for vitamins A and E and visible absorbance for β-carotene. An attribute of the method is the use of retinol propionate, α-tocopheryl propionate and all-E-β-apo-8'-carotenoic acid ethyl ester internal standards to compensate for analytical variations associated with these labile vitamins. Extraction is performed without saponification, with the aid of protease to remove vitamin encaspsulation and facilitate vitamin partition into hydrocarbon solvent. Figures of merit indicate the method is suitable for its intended purpose in the highly regulated infant formula environment, including liquid formulations. The method is extendable to whole milk powders where total vitamin A content data can be calculated by summing the innate long-chain vitamin A esters with the added esters.