Patent ID: 8084269

Claim:
A method for determining the amount of 1α,25(OH) 2 D 3 in a sample by mass spectrometry, the method comprising the steps of: ionizing 1α,25(OH) 2 D 3 from the sample to generate one or more 1α,25(OH) 2 D 3 ions detectable by mass spectrometry, wherein said one or more 1α,25(OH) 2 D 3 ions comprise one or more ions selected from the group consisting of ions with a mass-to-charge ratio of 381.1±0.5, 109.0±0.5, 156.9±0.5, and 159.2±0.5; determining the amount of one or more of the 1α,25(OH) 2 D 3 ions by mass spectrometry; and relating the determined amount of 1α,25(OH) 2 D 3 ions to the amount of 1α,25(OH) 2 D 3 in the sample.