Measurement of conversion yield of 7-dehydrocholesterol to previtamin D using liquid chromatography-mass spectrometry

Abstract

Vitamin D is involved in many diseases including sleep disorders, bone metabolism, diabetes, and multiple sclerosis. It is formed from 7-dehydrocholesterol (7-DHC) present in the human skin. When 7-DHC receives UV-B (280-315 nm), it becomes previtamin D and then is converted to vitamin D by thermal isomerization. Herein, we report an analytical method to quantify the conversion yield of vitamin D from 7-DHC by UV irradiation based on liquid chromatography-mass spectrometry (LC-MS), which has a higher selectivity compared with conventional LC-UV. In order to find optimal irradiation conditions, the conversion yields of 7-DHC to previtamin D were measured by varying irradiation time and light source wavelength. After 7-DHC was exposed to a UV-B source in vitro with light intensity of 0.5 mW / cm2 for 0-120 sec, 7-DHC, previtamin D, and vitamin D were separated on a Zorbax SB phenyl column and analyzed by a quadrupole-time-of-flight mass analyzer. The conversion yield of 7-DHC to previtamin D increased steadily with increasing irradiation time at all UV-B wavelengths and showed the maximum yield of 10% with UV-B irradiation for 120 sec at 285 nm.