Negative ion liquid secondary ion mass spectrometry and tandem mass spectrometric analysis of the molecular species of aminophospholipids as 9-fluorenylmethyloxycarbonyl derivatives

An approach has been developed for the analysis of aminophospholipids as 9-fluorenylmethyloxycarbonyl (Fmoc)-derivatized molecular species. Negative ion liquid secondary ion mass spectrometry of the derivatives of glyceropho-sphatidylethanolamine, glycerophosphatidylserine and their lyso analogous yields abundant [M-H]− ions and informative fragment ions ([R2COO]− and [R1COO]− as well as [M-polar head-R2COO]−, [M-polar head-R2CO-H]−, [M-Fmoc-polar head-R2COOH]− and [M-Fmoc-polar head-R2CO-H]−) for identifying the fatty acid chains. Conventional and collisionally induced dissociation mass spectra of the derivatized species exhibit fragmentation modes identical to those of their underivatized molecules, however, the ion patterns of both underivatized and derivatized glycerophosphatidylserine (GPS) are different from those of the relative glycerophosphatidylethanolamine (GPE) species, mainly in the intensity ratio of [R2COO]− and [R1COO]− carboxylate ions and abundances of [M-polar head-R2COOH]− and [M-polar head-R2CO-H]− as well as [M-Fmoc-polar head-R2COOH]− and [M-Fmoc-polar head-R2CO-H]− anions. The lower limit for producing a useful conventional and tandem mass spectrum of the derivatized aminophospholipid species is around 2 and 30 ng, respectively. The usefulness of this method has been demonstrated in the analysis of the molecular species of GPE and GPS from rat kidney. The approach will be ultilized in investigation on the metabolism of natural aminophospholipids.