Fast Atom Bombardment and Tandem Mass Spectrometry for Determining Structural Modification of Fatty Acids

Previous studies showed that coilisionally activated gas-phase carboxylate anions of saturated fatty acids undergo losses of the elements of CH₄, C₂H₆, C₃H₈,. by way of a highly specific 1,4-elimination of H₂. These C_nH_2n+2 losses begin at the alkyl terminus and progress along the entire alkyl chain. In this paper we report that the presence of a substituent such as an alkyl branch, hydroxy group, cyclopropane ring, cyclopropene ring, or epoxide ring interrupts this process in a characteristic fashion that permits Indentification of the substituent and location of its position on the acid chain. This method not only is useful for structural characterization of pure free fatty acids but also is applicable to the analysis of mixtures of carboxylic acids.