Ion mobility and tandem mass spectrometry of phosphatidylglycerol and bis(monoacylglycerol) phosphate (BMP)

• PG and BMP regioisomers were studied by tandem mass spectrometry with ion mobility.
• Precursor ions of a PG and BMP isomeric pair were indistinguishable by MS/IMS.
• Product ions in positive ion mode were distinctly different by MS/MS/IMS.
• Mechanisms of fragmentation were evaluated using deuterium labeling.
• PG and BMP species in RAW 264.7 cells were studied using MS/MS/IMS.

The tandem mass spectrometry, ion mobility, and normal phase HPLC of isomeric phosphatidylglycerol (PG) and bis(monoacylglycerol) phosphate (BMP) have been investigated in this study with the objective of differentiating these unique classes of lipids. Measurement of ion mobility using the traveling wave method for negative molecular and product ions from isomeric PG and BMP yielded identical results, but different ion mobilities were observed for positive product ions arising from collision-induced dissociation (CID). The fastest moving positive product ions from the ion mobility analysis of BMP(18:1/18:1) were monoglyceride-like, and the slowest moving product ions from this BMP corresponded to [M + H − 2H2O]+, which were readily observed for BMP but were only at very low abundance in the CID spectra of PG. The major product ions observed from the sodium adduct of PG(18:1/18:1) were consistent with diglyceride-like ion formation, but for BMP(18:1/18:1) only monoglyceride-like product ions were formed. The usefulness of ion mobility separation was tested with the selection of positive product ions derived from the isomeric PG and BMP molecular species in the lipid extract of RAW 264.7 cells. The ion mobility spectra of monoglyceride-like ions derived from BMP species with various esterified fatty acyl groups displayed some separation in ion mobility based on fatty acyl chain length and presence of a double bond in the acyl chain. The mechanism of ion formation of the diglyceride- and monoglyceride-like ions from PG and BMP respectively was examined using deuterium-labeled species including PG(D3116:0/18:1) and PG and BMP labeled by deuterium exchange.

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