Synthetic carotenoids as internal standards for plasma micronutrient analyses by high-performance liquid chromatography.

A method is described for the synthesis of new carotenoids by transesterification of ethyl-beta-apo-8'-carotenoate. The rate of transesterification was temperature-dependent with highest yields using primary alcohols. Reaction conditions were found avoiding Z isomerization. The structures of the new products were confirmed by ultraviolet, mass, 1H and 13C nuclear magnetic resonance spectroscopy. The synthetic carotenoids were used as internal standards for reversed-phase high-performance liquid chromatographic (HPLC) analyses of lipid phase plasma micronutrients. Retention times for the trans-esterified products increased as a function of alcohol chain length allowing a choice of synthetic carotenoids for use as internal standards for carotenoid quantitation without interference with the detection of analytes during HPLC analysis.