2.6. Instrument Parameters

Using LC-MS/MS to establish a quantitative analysis method of 5 linoleic acid oxides through multi-reaction monitoring (MRM) mode [28]. The mass spectrometry parameters are as follows: scanning mode is ESI negative ion mode, ion source temperature 120 °C, capillary voltage 30 V, cone voltage 30 V. Nitrogen was used as cone gas (with flow rate 50 L/h) and desolvation gas (with flow rate of 40 L/h at 350 °C). Argon was used as the collision gas at a flow rate of 0.2 mL/min to induce fragmentation for MS/MS analysis.

Chromatography parameters: the water phase of the mobile phase A is 0.1% formic acid solution, the organic phase of the mobile phase B is acetonitrile, the column temperature is 50 °C, the sample volume is 2 μL, and the flow rate is 0.35 mL/min. The elution conditions are: 0 min, A/B (60:40); 1 min, A/B (60:40); 7 min, A/B (30:70); 8 min, A/B (1:99); 10 min, A/B (1:99); 10.1 min, A/B (60:40); 13 min, A/B (60:40). The mass spectrometry parameters and chromatographic peak of the oxides to be measured are shown in Table 2 and Figure 1 below.

Mass spectrometric parameters of 5 linoleic acid oxides.

^a Q1, parent ion. ^b Q3, fragment ion. ^c DP, declustering potential. ^d CE, collision energy.

LC–MS/MS chromatograms of 1000 μg/L of 5 linoleic acid oxide standards in the MRM mode; (a) 9,12,13-trihydroxy-10(E)-octadecenoic acid (THO); (b) 9,10-Dihydroxy-12-octadecenoic acid (DHO); (c) 9-oxo-(10E,12Z)-octadecadienoic acid (OXO); (d) 9-hydroxy-(10E,12Z)-octadecadienoic acid (9HO); (e) 13-hydroxyoctadeca-(9Z,11E)-octadecadienoic acid (13HO). The numbers in the graph represent the retention time (RT).