Additional file 1: Figure 1S. (a): Freeze thaw stability of QC med at three cycles (n = 3). (b): Autosampler stability of QC med at ambient temperature (n = 3) A) after 6, 9, 14 and 24 hours. Figure 2S. Stability of calibration of QC low and QC high of (a) camphene, (b) β-pinene, (c) 3-carene, (d) limonene, (e) β-caryophyllene and (f) borneol over six validation days calculated with the calibration equation of the first day. The dotted lines represent an error of ±20%. Figure 3S. Chromatographic profiles of GC-FID of (a) CEO1 (Pinus sylvestris L.) with 1) α-pinene, 2) camphene, 3) β-pinene, 4) 3-carene, 5) limonene, 6) cis-3-hexenol (IS) and 7) bornyl acetate. Figure 4S. Chromatographic profiles of GC-FID of CEO15 (Abies sibirica L.) with 1) α-pinene, 2) camphene, 3) β-pinene, 4) 3-carene, 5) limonene, 6) cis-3-hexenol (IS), 7) bornyl acetate, 8) β-caryophyllene and 9) borneol. Table 1S. Name, in-house code, charge and supplier of the commercial EOs. Table 2S. Chemical properties of the used terpenes and preparation of the stock solutions for Cal and QC samples (dilution solvent: first 2 mL EtOH, then ad 20 mL with heptane) and of the IS. Table 3S. Serial dilution for the Cal and QC samples. Table 4S. Concentrations for Cal and QC samples. All concentrations are given in [mM]. Table 5S. Method validation data: calibration curve, R2, linear range, retention time robustness and back-calculation of the Cal (n = 6). Data calculated with the RRF are in bold. Table 6S. Long-term stability (1 month) of processed CAL and QC samples at –20 °C (n = 2). Stock solution stability of the CAL are in bold, n.d. = not determined. Table 7S. Chemical composition (%, percentages of the total EO composition), -: not detected (peak area < 5000 or not present).