Structural analysis of oligomeric molecules formed from the reaction products of oleic acid ozonolysis.

The products arising from the ozonolysis of oleic acid (cis-9-octadecenoic acid) in solution have been studied using negative ion mode electrospray ionization ion trap mass spectrometry. Oleic acid is an important component of atmospheric organic aerosol and is a key model species in predicting aerosol physical and chemical characteristics. The four predicted reaction products, 1-nonanal, nonanoic acid, 9-oxononanoic acid, and azelaic acid, were all observed in roughly equal yields. In addition to these products a large number of higher molecular weight compounds were detected with m/z ratios of up to 1000 Daltons. Tandem mass spectrometry of these larger ions revealed thatthey represented a complex mixture of linear alpha-acyloxyalkyl hydroperoxides, secondary ozonides, and cyclic diperoxides, formed by reactions between ozonolysis products and Criegee intermediates. These comprise the first directly elucidated structures of large oligomeric species from oleic acid ozonolysis. The degree of oligomerization and hence molecular weight distribution was observed to increase with reaction time in solution.