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