FAB MS/MS for phosphatidylinositol, -glycerol, -ethanolamine and other complex phospholipids

Fast atom bombardment (FAB) of phosphatidylinositol, phosphatidylethanolamine, cardiolipin, phosphatidic acid and phosphatidylglycerol produces a limited number of very informative negative ions. Especially significant is the formation of (M-H)-ions and ions that correspond to the carboxylate portions of these molecules. FAB desorption in combination with collisional activation allows for characterization of fragmentation and determination of structural features. Collisional activation of the carboxylate anion from complex lipids is especially informative. Structural characterization of the fatty acids can be achieved as the released saturated carboxylate anions undergo highly specific charge remote fragmentations that are entirely consistent with the chemistry of carboxylate anions desorbed from free fatty acids. This permits both identification of the modification and assignment of its location on the acid chain. FAB-desorbed alkyl acetyl glycerophosphocholines (platelet-activating factor) do not produce (M-H)-ions. However, significant high mass ions are formed, and these can be collisionally activated for structural characterization.