High pressure liquid chromatographic determination of vitamin D3 in instant nonfat dried milk.

Vitamin D3 was determined in commercially fortified instant nonfat dried milk by using normal phase high pressure liquid chromatography (HPLC). The sample was extracted with dichloromethane with sodium phosphate tribasic solution added. The sample was cleaned up by using a Sep-Pak silica cartridge and then a microparticulate column containing 10 micrometer Partisil-10 PAC packing material. The final analysis was performed by using a normal phase HPLC system with 10 micrometer LiChrosorb NH2 column. Recovery of vitamin D3 at levels as low as 10000 IU/kg was 97.7% with a standard deviation of 3.9%.