High performance liquid chromatographic determination of vitamin D in fortified milks, margarine, and infant formulas.

Fortified milks were saponified overnight at room temperature with 1% ethanolic pyrogallol and KOH. The digest was extracted with hexane after adding water and ethanol, and the extract was washed consecutively with 5% KOH, water, and 55% aqueous ethanol to remove polar lipids. After evaporation, the residue was first chromatographed on a column of 5 micrometer silica. A fraction containing vitamin D was collected, evaporated, and rechromatographed on a reverse phase column for the separation and quantitation of vitamins D2 and D3. Recovery was 96-99% and the coefficient of variation was 3% (8 replicates). Infant formula was diluted and then saponified and extracted as in the analysis of milk. Margarine was saponified by shaking overnight with 1% ethanolic pyrogallol and 80% KOH. Water and ethanol were added to the digest before extraction. Extracts from formula and margarine were chromatographed as milk except, before HPLC, the extract was dissolved in isopropanol-hexane (1 + 99) and passed through 5 cm alumina in a Pasteur pipet, and the concentration of isopropanol in the first high performance liquid chromatographic (HPLC) solvent system was halved to improve the separation of vitamin D from other absorbing lipids. Usually several peaks were obtained during the final HPLC analysis, and the identification of vitamins D2 and D3 was less certain than in the analysis of milk. The coefficients of variation for formula and margarine were 6% (5 replicates) and 9% (6 replicates), respectively.