We describe a highly sensitive method for the detection of 7-dehydrocholesterol (7-DHC),
the biosynthetic precursor of cholesterol, based on its reactivity with 4-phenyl-1, 2, 4-
triazoline-3, 5-dione (PTAD) in a Diels-Alder cycloaddition reaction. Samples of biological
tissues and fluids with added deuterium-labeled internal standards were derivatized with
PTAD and analyzed by LC-MS. This protocol permits fast processing of samples, short
chromatography times, and high sensitivity. We applied this method to the analysis of cells …