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

Negative ion electrospray ionization mass spectrometry combined with collisional 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 fragments 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 orders 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 corresponding [M - H](-) species: in the presence of S-34, the fragment ions split into doublets, whereas the fragment ions of phosphate esters remain monoisotopic signals, Cholesterol 3-sulfate is identified and quantitated from total lipid extracts of mouse skin keratinocytes without chromatographic separation and using dihydrocholesterol 3-sulfate as internal standard. During epidermal differentiation, the level of cholesterol 3-sulfate increases from about 16 ng/10(6) cells found in basal cells to about 400 ng/10(6) cells observed in the most differentiated cells.