Rapid Quantitation of 25-Hydroxyvitamin D2 and D3 in Human Serum Using Liquid Chromatography/drift Tube Ion Mobility-Mass Spectrometry

Ion mobility was integrated with liquid chromatography/high resolution mass spectrometry (LC/IM-HRMS) to quantify 25-hydroxyvitamin D (25OHD) in human serum. It has previously been shown that 25OHD adopts two gas-phase conformations which are resolved using ion mobility; in contrast, the inactive epimer, 3-epi-25-hydroxyvitamin D (epi25OHD), only adopts one. Interference from epi25OHD was eliminated by filtering the chromatogram to retain the drift time that corresponds to the unique gas-phase conformation of 25OHD. Although ion mobility separates the epimers, some chromatography is required to separate compounds which interfere with ionization or fall at the same nominal m/z. Standards were prepared in 4% albumin solutions and compared against commercial serum quality controls. Standards and quality controls were analyzed and validated using a 2 min LC/IM-MS method. 25-Hydroxyvitamin D3 and D2 were quantified over the range between 2 and 500 ng/mL with bias and precision within 15%. When epi25OHD was spi...