Chiral-phase high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry of 1-O-alkylglycerols derived from muscle lipids of Stromateus stellatus

The chirality and molecular species of 1-O-alkylglycerols derived from muscle lipids from a Stromateidei fish, Stromateus Stellatus, were determined by chiral-phase high-performance liquid chromatography (HPLC) and mass spectrometry (MS). For this purpose, 1-O-alkylglycerols were derived from 1-O-alkyl-2,3-diacylglycerols by methanolysis and were then converted into bis-3,5-dinitrophenylurethane (DNPU) derivatives. These were then analyzed by chiral-phase HPLC in conjunction with atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The HPLC separation was performed on a column (25 cm x 4.6 mm i.d., 5 microm particle size) having a chiral phase of N-[(S)-1-(1-naphthyl)ethylaminocarbonyl]-(S)-tert-leucine and using hexane/dichloromethane/ethanol 40 : 12 : 4, by vol) as the mobile phase. The APCI-MS was carried out using an iontrap mass spectrometer. Post-column addition of 2-propanol was used to assure APCI in the negative mode. In addition to a prominent solvent adduct ion [DNPU+CH3CH(OH)CH3-H]sup(-) (base peak), the spectra showed [M-DNPU]sup(-), [M-DNPU+Cl]sup(-) and [M+Cl]sup(-) ions, from which the major molecular species could be identified. The results clearly showed that the glycerol moieties in all the alkylglycerols had an S-configuration (sn-1-O-) and that the major molecular species were 14 : 0, 16 : 0, and 18 : 1. The fragment ions related to the minor components (18 : 0, 16 : 1, 17 : 0 and 20 : 1), which were previously detected by chiral-phase HPLC/electrospray ionization MS [Yamashina, Lee and Itabashi : Bunseki Kagaku, 55, 643-650 (2006)], were not observed under the conditions employed. Thus, the present method demonstrates that the chiral-phase HPLC/APCI-MS provides unambiguous information about the chirality and can be used for identification of the major molecular species of natural 1-O-alkylglycerols.