Calorimetric method for the determination of vitamin D in fortified whole and partially skim fluid milks
Panalaks, T.
Journal - Association of Official Analytical Chemists 54(6): 1299-1303
1971
ISSN/ISBN: 0004-5756 PMID: 5172632 Document Number: 37459
Vitamin D in fortified milk was determined from a standard curve prepared from the addition of known amounts of the vitamin to unfortified milk. The usual exhaustive extractions for isolation of the unsaponifiable fraction were replaced by a labor-saving benzene partition technique. The main interfering substance, cholesterol, was removed by passing the sample extract through a column of Celite impregnated with digitonin. Other interfering substances were removed by partition and adsorption column chromatography. Oxidative deterioration of the vitamin during saponification and subsequent analytical steps was prevented by additions of antioxidants and by addition of a high boiling hydrocarbon to prevent drying. The vitamin concentration was determined colorimetrically at 500 nm after reaction with antimony trichloride, using a correction factor derived from absorbances measured at 435 and 550 nm. The use of a color inhibitor was eliminated. The method when applied to whole and partially skim milks fortified with vitamin D in the range from 22 to 44 IU/100 ml milk gave recoveries of 92 and 103%, respectively.