LC-MS/MS-MRM-Based Targeted Metabolomics for Quantitative Analysis of Polyunsaturated Fatty Acids and Oxylipins

LC-MS/MS with multiple reaction monitoring (MRM) is a powerful tool for targeted metabolomics analysis including screening and quantification of known metabolites. Given the complexity of biological samples, the difference in ionization efficiency, and signal intensity of each metabolite, isotopically labeled internal standards are often used for accurate quantification. In this chapter, we describe a detailed protocol for the quantitative analysis of polyunsaturated fatty acids (PUFAs) and their oxidized products (oxylipins) by LC-MS/MS-MRM with isotope dilution. PUFAs are very susceptible to oxidation by both enzymatic and nonenzymatic pathways. Free PUFAs and corresponding oxylipins, known as bioactive lipids, are involved in many processes with varying biological functions depending on their chemical structure and concentration. Accurate quantification is thus becoming crucial to understanding the role of these bioactive lipids in health, disease(s), and other settings.