Convenient analysis of vitamin D in cheese and other food matrixes by liquid chromatography/mass spectrometry.

A convenient method is presented for determination of vitamin D in natural cheese, processed cheese, milk, cereals, noncarbonated soft drinks, and juice by liquid chromatography/ mass spectrometry (LC/MS). Samples were saponified, extracted, evaporated, redissolved in acetonitrile, and injected into an LC-atmospheric pressure chemical ionization-MS system with no preparative chromatographic steps. Vitamin D was determined by selected ion monitoring. MS response was linear for vitamin D3 and its internal standard vitamin D2, and overall average recoveries ranged from 98 to 105%. A blending experiment in which shredded vitamin D3-fortified cheddar was mixed with control nonfortified cheddar showed linearity. The limit of detection for vitamin D was 1.3 ng and the limit of quantitation was 3 ng. The method gave good accuracy and precision, with a standard deviation of 9.5 and relative standard deviation of 6.7%. Results for vitamin D3 obtained with this method for different food matrixes, at different levels, were in agreement with those obtained with the reference LC/UV method currently used by many laboratories and derived from AOAC Official Method 982.29.