Free Radical Activated Fatty Acid Sequencing Mass Spectrometry for Fatty Acid Characterization

Fatty acids are critical components in cells and are involved in a variety in extracellular and interstellar processes. Numerous human diseases have been correlated to abnormal fatty acid metabolism. Fatty acids have been traditionally difficult to study due to their complex structures, various levels of saturation, varying head groups, and properties. Electron-activated dissociation (ExD) techniques, nuclear magnetic resonance (NMR), and collision-induced dissociation are some of the forefront methods used for fatty acid characterization. However, these techniques are unable to provide a complete profile for fatty acid structure elucidation. We have previously demonstrated the use of synthesized reagents that have given powerful qualitative and quantitative structural information of a variety of bio molecules such as glycans and peptides. We have extended our range of analysis to fatty acids employing similar techniques previously done. We use a Free Radical Activated Fatty Acid Sequencing Elucidation (FRAASE) reagent chemically coupled to a fatty acid's carboxylic tail which is then directly injected to an electrospray ionization source of a Thermo LTQ-XL mass spectrometer at a rate of 5uL/min in positive ion mode. The derivatized fatty acid undergoes collision induced dissociation where the TEMPO precursor component of FRAASE undergoes homolytic cleavage to generate the nascent free radical. Upon MS/MS and MS/MS/MS, radical driven fatty acid backbone fragmentation is observed and characterized. We have thus far been able to achieve complete and systematic fragmentation of saturated fatty acids and studies are currently being performed on polyunsaturated fatty acids.