Mass spectrometry of isomeric fatty acid hydroperoxides by chemical ionization via direct exposure probe

Intact isomeric methyl 9- and 13-hydroperoxy linoleates are analyzed by chemical ionization (CI) mass spectrometry using a direct exposure probe. Both isobutane and ammonia CI spectra were obtained. With isobutane CI, ions are observed for protonated fragments that are indicative of an acid catalysis mechanism similar to that observed in solution, whereas ammonia CI yields primarily adduct ions. The collisionally activated decomposition daughters of the high mass ions can be used to identify the position of the hydroperoxy group in the isomers studied.