Simultaneous determination of fat-soluble vitamins and provitamins in dairy products by liquid chromatography with a narrow-bore column

A reversed-phase high-performance liquid chromatographic method is describe d for the simultaneous determination of vitamins A, D-2, D-3, E and K-1, re tinyl acetate, retinyl palmitate, tocopherol acetate, ergosterol and 7-dehy drocholesterol in milk and butter. Narrow-bore columns are recommended beca use this alternative provides a good separation and efficiency, plus greate r economy and sensitivity. Detection limits for individual vitamins range f rom 0.14 to 6.9 ng. All vitamins are separated in less than 33 min. For the simultaneous determination of these vitamins and provitamins we use two sa mple pre-treatment methods, a liquid-liquid extraction with hexane or a sol id-phase extraction with a C-18 cartridge. Recovery studies show good resul ts for all solutes (84-108% and 85-108% for milk and butter, respectively) and the intra-day coefficients of variations range from 1.6 to 4.5%. These methods permit the simple determination of fat-soluble vitamins using a sma ll sample volume.