Mass spectrometric determination of non-derivatized, non-metabolized vitamin d

A method for determining the amount of non-metabolized vitamin D3 in a sample by tandem mass spectrometry, the method comprising the steps of:

• (i) subjecting non-metabolized vitamin D3 from a sample to an ionization source under conditions suitable to generate one or more precursor ions comprising a mass to charge ratio (m/z) of 367.2±0.5;
• (ii) fragmenting at least one of said precursor ions to generate one or more fragment ions detectable by mass spectrometry, wherein the fragment ions comprise one or more ions selected from the group consisting of ions with m/z of 172.2±0.5, 145.0±0.5, and 119.1±0.5;
• (iii) determining the amount of one or more of the fragment ions generated in step (ii) by mass spectrometry;
• and
• (iv) relating the presence of non-metabolized vitamin D3 ions determined in step (iii) to the presence of non-metabolized vitamin D3 in the sample.