Quantitative high-performance liquid chromatographic method for determining the isomer distribution of retinol (vitamin A1) and 3-dehydroretinol (vitamin A2) in fish oils.

Seven retinol and seven 3-dehydroretinol geometric isomers were simultaneously fractionated on a silica column using a ternary mobile phase (2-propanol-1-octanol-n-hexane, 0.2:3.8:96). The method was applied to determine vitamin A active compounds present in fish oils. The standard additions method was used to obtain the recovery of the analytes, which was found to be the same for vitamin A1 and A2 (89%). Correction factors for determining all isomers when the peak areas are integrated at 326 nm are reported, so that the quantitative determination may be reproduced by others using the proposed method, which allows all data to be referred to the calibration graph of all-trans-retinol only. As every isomer is quantified separately, the method also permits the determination of the real vitamin A biopotency of the samples.