Structural analysis of hydroxy fatty acids by thermospray liquid chromatography/tandem mass spectrometry

Thermospray liquid chromatography/tandem mass spectrometry provides a sensitive and convenient technique for the structural analysis of oxygenated polyunsaturates. Analysis of pentafluorobenzyl derivatives in the negative ion mode under the filament- or discharge-on condition generated abundant [M - PFB]- ions. These ions were further fragmented by collision with argon and detected in the negative ion mode. The negative ion fragmentation pattern was examined for various oxygenated polyunsaturated fatty acid standards as well as their deuterated and/or hydrogenated forms. Characteristic fragmentation occurs at the oxygenated C-C bonds, allowing unambiguous determination of the sites of oxygenation. The sample amount required is typically in the low tens of nanogram range. Using this method the structures of epoxy, hydroxy derivatives of 4,7,10,13,16,19-docosahexaenoic acid (22:6w3) formed by soybean lipoxygenase were determined. They were 13-hydroxy-16,17-epoxy-22:5w3 and 15-hydroxy-16,17-epoxy-22:5w3.