Fragmentation Patterns of Fatty Acids and Modified Fatty Acids

Fatty acid (FA) represents a broad family of lipids containing at least one carboxylic acid group and a long aliphatic chain, which includes nonesterified and modified FA species. This chapter summarizes the electrospray ionization mass spectrometry (ESI-MS) - based efforts to characterize individual FA species with or without derivatization. The product-ion ESI mass spectra produced from monounsaturated FA species are relatively simple to interpret with the fragment ions located at the high end of m/z, which are produced from the cleavage of the single bond on the carboxylate side of the C-C double bond. Numerous modified nonesterified FA (NEFA) species are present in nature, including oxygenated, nitrosylated, halogenated species, etc. All these modifications are generated through enzymatic or nonenzymatic reactions which play many essential roles in biological systems. Charge-remote fragmentation has been well recognized as an effective approach for dissociation of long aliphatic chains.