Quantification of 25-Hydroxyvitamin D2 and D3 Using Liquid Chromatography-Tandem Mass Spectrometry.

Vitamin D plays an important role not only in bone health but also in many other body functions. Vitamin D deficiency is very common in the general population. Measurement of blood 25-hydroxyvitamin D is a common practice to evaluate vitamin D deficiency. Immunoassays and liquid chromatography tandem mass spectrometry (LC-MS/MS) are the most commonly used methods for the measurement of 25-hydroxyvitamin D. Immunoassays suffer from specificity issues and do not distinguish between 25-hydroxyvitamin D2 and D3. Therefore, LC-MS/MS is a preferred method for quantification of 25-hydroxyvitamin. We describe an LC-MS/MS method, which involves protein precipitation and analysis of the extract using atmospheric pressure chemical ionization and multiple reaction monitoring. 25-hydroxyvitamin D3-d6 is used as an internal standard. The method is linear from 1-100 ng/mL for both 25-hydroxyvitamin D2 and D3 and has imprecision of <10%.