GC analyses were performed on an Agilent 6890 (Agilent, Waldbronn, Germany) gas chromatograph coupled to an Agilent 5973 quadrupole mass selective spectrometer equipped with an inert ion source. The helium carrier gas was maintained at a constant flow of 1 mL min−1. An HP-5MS (5% phenyl 95% dimethylpolysiloxane, Agilent) capillary column (30 m × 0.25 mm i.d., 0.25 μm film thickness) was used.
The GC temperature was programmed as follows: start temperature of 75 °C (held 0.5 min) and increase to 275 °C at 20 °C min−1 (held 4.5 min). The total analysis time for one GC run was 15 min. The ionisation was carried out in the electron-impact (EI) mode (70 eV). The identity of the compounds was confirmed by comparison of retention time and MS-spectra with respect to pure standards. The analytes were quantified under the selected ion monitoring (SIM) mode using the target ions