Matrix-assisted laser desorption/ionixation high-energy collision-induced dissociation of steroids: analysis of oxysterols in rat brain

Abstract

Matrix-Assisted Laser Desorption/Ionization High-Energy Collision-Induced Dissociation of Steroids: Analysis of Oxysterols in Rat Brain Yuqin Wang, Martin Hornshaw, Gunvor Alvelius, Karl Bodin, Suya Liu, Jan Sjövall, and William J. Griffiths* The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, U.K., Applied Biosystems, Warrington, U.K., and Department of Medical Biochemistry & Biophysics, Karolinska Institutet, Stockholm SE 171 77, Sweden Received for review August 14, 2005. Accepted October 24, 2005. Abstract: Neutral steroids have traditionally been analyzed by gas chromatography/mass spectrometry (GC/MS) after necessary derivatization reactions. However, GC/MS is unsuitable for the analysis of many conjugated steroids and those with unsuspected functional groups. Here we describe an alternative analytical method specifically designed for the analysis of oxosteroids and those with a 3-hydroxy-5 or 5-hydrogen-3-hydroxy structure. Steroids were derivatized with Girard P (GP) hydrazine to give GP hydrazones, which are charged species and readily analyzed by matrix-assisted laser desorption/ionization mass spectrometry. The resulting [M]+ ions were then subjected to high-energy collision-induced dissociation on a tandem time-of-flight instrument. The product ion spectra give structurally informative fragment ion patterns. The sensitivity of the analytical method is such that steroid structures can be determined from low-picogram (low-femtomole) amounts of sample. The utility of the method has been demonstrated by the analysis of oxysterols extracted from rat brain.