GC-MS/MS analysis was performed employing a Thermo Scientific Trace 1310 gas chromatograph coupled to a triple quadrupole mass spectrometer (TSQ 8000) with an autosampler IL 1310 from Thermo Scientific (San Jose, CA, USA). Instrumental GC-MS/MS conditions were previously optimized by the authors [24 (link)]. Separation was carried out on a Zebron ZB-Semivolatiles (30 m × 0.25 mm i.d. × 0.25 μm film thickness) obtained from Phenomenex (Torrance, CA, USA). Helium (purity 99.999%) was used as carrier gas at a constant flow of 1 mL min−1. The GC oven temperature was programmed from 60 °C (held 1 min), to 100 °C at 8 °C min−1, to 150 °C at 20 °C min−1, to 200 °C at 25 °C min−1 (held 5 min), to 220 °C at 8 °C min−1 and finally to 290 °C at 30 °C min−1 (held 7 min). The total run time was 30 min. The injector temperature was set at 270 °C working in pulsed split/splitless mode (200 kPa, held 1.2 min).
The mass spectrometer detector (MSD) was operated in the electron impact (EI) ionization positive mode (+70 eV). The temperatures of the transfer line, and the ion source were set at 290 and 350 °C, respectively. The filament was set at 25 μA and the multiplier voltage was 1950 V. Selected reaction monitoring (SRM) acquisition mode was used, monitoring 2 or 3 transitions per compound (seeTable S1 ). The system was operated by Xcalibur 2.2, and Trace Finder™ 3.2 software.
The mass spectrometer detector (MSD) was operated in the electron impact (EI) ionization positive mode (+70 eV). The temperatures of the transfer line, and the ion source were set at 290 and 350 °C, respectively. The filament was set at 25 μA and the multiplier voltage was 1950 V. Selected reaction monitoring (SRM) acquisition mode was used, monitoring 2 or 3 transitions per compound (see