Instrumental analysis was performed with a gas chromatograph coupled to a mass spectrometer (GC-MS Shimadzu QP2010 Ultra) equipped with an AOC-20i/s autosampler. An HP-5 MS column (30 m ✕0.25 mm, film thickness: 0.25 μm) was used for separation. The initial oven temperature was set at 100 °C, then raised to 110 °C with a heating rate of 4 °C/min. The temperature was finally raised to 280 °C at 15 °C/min and held for 15 min. Injection volume was 2 μl in splitless mode and helium was employed as carrier gas (purity ≥ 99,999%) with a constant flow of 1.0 ml/min. The temperature of the ion source was 230 °C. The MS was operated in single ion monitoring (SIM) mode and the mass traces acquired (m/z) for each congener and IS are reported in Table 1.Table 1. Analytical and validation parameters of the applied method.