IDENTIFICATION AND QUANTIFICATION OF LIPID SULFATE ESTERS BY ELECTROSPRAY-IONIZATION MS MS TECHNIQUES - CHOLESTEROL SULFATE/

Negative ion electrospray ionization mass spectrometry combined with c ollisional activation is used for specific detection of sulfate esters in the presence of phosphomonoesters and phosphodiesters. The energy dependence for the formation of the relevant collision-induced fragmen ts ions is investigated. Sulfomonoesters give rise to a specific [SO3] (-) fragment at m/z 80, whereas phosphomonoesters generate a specific [PO3](-) fragment at m/z 79 and a specific [PO2](-) fragment at m/z 63 , In addition, both sulfo- and phosphomonoesters generate an isobaric fragment ion at m/z 97, with the composition [HSO4](-) or [H2PO4](-), respectively, Phosphodiesters generate this fragment ion with 2-3 orde rs of magnitude lower relative abundance compared to phosphomonoesters . A clear discrimination between sulfo- and phosphoesters was achieved by product ion analysis of the M + 2 satellite ion of their correspon ding [M - H](-) species: in the presence of S-34, the fragment ions sp lit into doublets, whereas the fragment ions of phosphate esters remai n monoisotopic signals, Cholesterol 3-sulfate is identified and quanti tated from total lipid extracts of mouse skin keratinocytes without ch romatographic separation and using dihydrocholesterol 3-sulfate as int ernal standard. During epidermal differentiation, the level of cholest erol 3-sulfate increases from about 16 ng/10(6) cells found in basal c ells to about 400 ng/10(6) cells observed in the most differentiated c ells.