HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND LASER-DESORPTION IONIZATION MASS-SPECTROMETRY OF RETINYL ESTERS

Laser desorption/ionization mass spectrometry (LDI-MS) at 337 nm laser wavelength was used to analyze retinol and several long-chain fatty a cid esters of retinol, Employing this ionization technique helped to o vercome the inherent problems resulting from thermal instability of re tinyl esters which render this group of compounds rather difficult for standard ionization techniques, Mass spectra were recorded with a lin ear time-of-flight instrument in positive ion mode. Under these condit ions, retinyl esters formed radical molecular ions (M.+) and in additi on fragmented by elimination of the fatty acyl chain to uniformely for m a peak at m/z = 269 u. The elimiation of carbon dioxide was also obs erved in the spectra, The method is suitable to identify specific reti nyl esters in complex mixtures of these compounds. A gradient reversed -phase high-performance liquid chromatography (HPLC) is described for the separation of retinol and 15 related fatty acid esters within 28 m in, HPLC was applied to separate retinyl esters from rat liver extract s, The LDI mass spectrum of the collected HPLC fraction of rat liver e xtract showed the molecular parent ions of retinyl myristate, pentadec anoate, palmitoleate, palmitate, heptadecanoate, linoleate, oleate, st earate, and 3,4-didehydroretinyl palmitate. LDI-MS was found to be mor e appropriate than matrix-assisted laser desorption/ionization for the described analytical task.