Rapid Determination of Free Fatty Acids in the Extracellular Medium of Cyanobacteria by Stir Bar Sorptive Extraction (SBSE) Coupled to Ultra-High-Performance Liquid Chromatography – Triple Quadrupole Tandem Mass Spectrometry (UHPLC-MS/MS)

A rapid and sensitive method was developed determine free fatty acids in cyanobacteria extracellular medium without derivatization by stir bar sorptive extraction (SBSE) coupled to ultra-high-performance liquid chromatography – tandem mass spectrometry (UHPLC-MS/MS). The stir bars (20 mm in length and 1 mm in film thickness) coated with polydimethylsiloxane was used to directly extract 11 free fatty acids (C14-C24) in cyanobacteria extracellular media. The performance was optimized, including the column, temperature, extraction time, organic modifier, and desorption solvent. Limits of detection and quantification, precision, and linear dynamic ranges for the free fatty acids were evaluated. The method was applied to determine free fatty acids in cyanobacteria extracellular media at the exponential and plateau phases. Eicosanoic acid (C20:0), linoleic acid (C18:2), oleic acid (C18:1), stearic acid (C18:0), palmitic acid (C16:0) and myristic acid (C14:0) were quantified in the samples.