4.7. Fatty Acid Analysis by GC-MS

For the gas chromatography–mass spectrometry (GC-MS) analysis of C14 to C26 fatty acids, collected samples were extracted by the Folch method and derivatized using acetyl chloride. The C19:0 was used as the internal standard. All analyses were performed in spitless mode using an Agilent 7890a gas chromatograph connected to an Agilent 5975C Series mass. selective detector (MSD) (Agilent, Santa Clara, CA). The chromatographic columns were 30 m DB-5 MS + DG capillary columns (5% phenyl, 95% dimethylpolysiloxane), with an internal diameter of 250 μm (Agilent, Santa Clara, CA). The injection volume was 1 μL. The oven temperature began at 60 °C for 1 min and was then increased to 160 °C at a rate of 30 °C min⁻¹, followed by a further increase to 260 °C at a rate of 2 °C min⁻¹, then to 300 °C at 5 °C min⁻¹, which was maintained for 1 min. The equilibration time between injections was 2 min. The electron impact ionization was 70 eV. The MS source and MS quadrupole were maintained at 230 °C and 150 °C, respectively. The masses of the analysis were acquired in full scan mode with a mass range of 30–650 m/z.