Analysis of fatty acids with GC–MS

Separately, 0.1 g of the four E. ulmoides seed oils were added to 1.0 mL of NaOH-CH₃OH solution at a concentration of 0.50 mol/L, shaken well, and reacted in a 60 °C water bath for 30 min until the oil droplets disappeared completely. Then, 1 mL boron trifluoride methanol solution (0.5 mol/L) was added, and the sample was placed in a water bath at 80 °C for 5 min. The sample could cool naturally to 25 ± 1.5 °C, before 1.60 mL of n-hexane was added to the test tube, and it was shaken vigorously for extraction. The mixture could stand to clarify it, and the supernatant was collected for GC–MS analysis.

The E. ulmoides seed oil fatty acid methyl ester was analyzed using an Agilent Technologies 7890B-5977A gas chromatography–mass spectrometer, with an HP-5MS quartz capillary column (30 m × 0.250 mm × 0.25 μm). The column and injection port temperatures were 50 °C and 280 °C, respectively. The temperature was held at 50 °C for 2 min, increased at 5 °C/min to 180 °C, held for 5 min, and then increased at 10 °C/min to 290 °C, and held for 3 min. The carrier gas was high-purity helium (99.999%), the flow rate was 1 mL/min, the pre-column pressure was 69.8 kPa, the split ratio was 10:1, and the injection volume was 1.0 μL. Mass spectrometry conditions: electron ionization ion source 230 °C, solvent delay 3 min, electron energy 70 eV, quadrupole temperature 150 °C, scanning range 40–500 m/z, multiresolution signal decomposition transmission line temperature 230 °C, and electron multiplier voltage 2300 V.

The compositions of the E. ulmoides seed oil fatty acids were determined by comparing them with a fatty acid methyl ester mixed standard and using National Institute of Standards and Technology (NIST 14 Mass Spectral Library) MS spectrum search and matching. The relative percentage of each fatty acid methyl ester in the sample is calculated by normalizing the peak area.