Determination of etretinate and its main metabolite in human plasma using normal-phase high-performance liquid chromatography.

An analytical method for the determination of two aromatic retinoids in human plasma (etretinate and its main metabolite) is described, using normal-phase high-performance liquid chromatography. The method is highly sensitive (4 ng/ml) and selective, and allows good separation of isomerization products. Both compounds are well extracted (95%) from plasma in the practically important concentration range (10--1000 ng/ml). After chromatographing the compounds together with an internal standard, they are quantified by spectrophotometry.