Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus

Electrospray ionization (ESI) combined with multiple‐stage tandem mass spectrometry (MSn) was used to directly analyze the glycolipid mixture from bacteria Bacillus pumilus without preliminary separation. Full scan ESI‐MS revealed the composition of picomole quantities of glycerolglycolipid species containing C14‐C19 fatty acids, some of which were monounsaturated. Two main components were identified from their molecular masses and fragmentation pathways. The fragmentation pathway of the known compound compared with the investigated compound verified the proposed structure as 1(3)‐acyl‐2‐pentadecanoyl‐3(1)‐O‐[β‐D‐glucopyranosyl‐(1→6)‐O‐β‐D‐glucopyranosyl]‐sn‐glycerols. A comparison of the multiple tandem mass spectra of the different alkali‐metal cation adducts indicates that the intensity of fragments and the dissociation pathways are dependent on the alkali‐metal type. The basic structures of glycerolglycolipids were reflected clearly from the fragmentation patterns of the sodium cations. The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct ions. ESI‐MSn spectra of [M + K]+ ions did not provide as much fragmentation as [M + Na]+ and [M + Li]+ adducts, but their spectra allow the position of glycerol acylation to be determined. On the basis of MS2 spectra of [M + K]+ ions, it was established that all components have a C15:0 fatty acid at the sn‐2 position of the glycerol backbone and C14‐C19 acids at the sn‐1 position of the glycerol backbone. Copyright © 1999 John Wiley & Sons, Ltd.