HS–SPME–GC–MS condition

Chemical analyses were conducted using HS–SPME–GC–MS (Shimadzu, QP-2010 Ultra, Japan) combined system, featuring an AOC-5000 automatic sampler for solid-phase microextraction injection (Supelco, SPME fiber assembly 65 μm PDMS/DVB, USA) and static, lipid headspace (Hamilton, 2.5 ml headspace syringe, Germany). Chromatographic separations employed a VF-WAXms capillary column (Agilent, CP9205, 30 m × 0.25 mm, 0.25 μm coating thickness, Germany), with sampling from 10 ml headspace bottles (GL Science, Japan) equipped with a magnetic cap and silicone/PTFE septum.

The GC–MS method was optimized for improved chemical separation with the following parameters. The column temperature was programmed as follows: 0 min at 40 °C, 5 °C/min to 100 °C and holding for 10 min, 5 °C/min to 110 °C and holding for 5 min, 5 °C/min to 190 °C, 10 °C/min to 130 °C and holding for 6 min. High-purity helium served as the carrier gas at a column flow of 1.2 ml/min, with a split ratio of 1:1, and an injection temperature of 230 °C. The spectrometers were operated in the electron-impact (EI) mode, with a scan range was m/z 35–500, a scan rate of 0.30 s per scan, and an ionization energy of 70 eV. The ion source and interface temperature were set at 200 °C and 230 °C respectively. The temperature and time of extraction (PDMS/DVB) were set at 70 ℃ for 30 min extraction of violent compounds in the OCs, followed by desorption at 250 ℃ for 3 min, utilizing a 2.5 mL syringe of headspace and a sampling time of 0.5 min.