Vitamin D in infant formula and enteral products by liquid chromatography: collaborative study.

Results from a collaborative study of a new liquid chromatographic (LC) method for determination of vitamin D in infant formulas and enteral products are presented. Each of 15 laboratories was provided with 11 blind duplicate samples covering a range of approximately 200-500 International Units/quart (normal dilution), a system suitability sample, and the U.S. Pharmacopeia ergo- and cholecalciferol standards. Product types included liquid and powder forms of milk (whey and casein), soy, and hydrolyzed protein-based infant formulas and enteral products. The method includes a single liquid-liquid extraction following saponification, solid-phase extraction, and then concentration by evaporation. An isocratic, nonaqueous, chromatographic system with reversed-phase, zero endcapped C18 column, and UV detector set at 265 nm are used. Statistical evaluation of data from participating laboratories show the average reproducibility and repeatability of the method across all samples to be excellent, with RSDR and RSDr values of 13.48 and 9.44, respectively, after elimination of outliers. The LC method for determination of vitamin D in infant formulas and enteral products has been adopted by AOAC INTERNATIONAL.