2.9. Gas Chromatography-Mass Spectrometry (GC-MS) Analysis

The basic steps of the experiment were as follows. The GC-MS analyses were carried out following the procedure described by Marek et al. [29]. A Trace GC Ultra gas spectrometer and an ITQ 1100 mass spectrometer were used as tools. Both devices were purchased from ThermoFisher Scientific (Waltham, MA, USA).

Before starting the tests, the column was calibrated with (C5-C24) (Supelco, Merck KGaA). The mixture of n-alkanes was analyzed for 1 μL of n-alkanes solution and analyzed. Alkane retention times obtained during the analysis were used to identify 138 tested standards in the Wiley library for the ZB-5MSplus Capillary GC 30 m × 0.25 mm × 0.25 μm column used. Such tests were performed because times could have varied due to, for example, poor column quality or the use of different gases as carriers therein. The obtained pattern retention times allowed for over 90% identification of the tested patterns in the Wiley 138 library, which was also used to identify the smells of the tested oil samples. The analyses were performed with programmed temperature: initial temperature 60 °C maintained for 5 min, from 60 to 250 °C at 5 °C/min, 250 to 270 °C at 10 °C/min, the final temperature being maintained for 5 min. The helium flow rate was held constant at 2.2 mL/min. The transfer line, ion source and quadrupole temperatures were 280 °C. Electron Ionization (EI₊) mode with an electron energy of 70 eV was used. The mass spectrometer acquired data in full scan mode (scan ranges: 35–390). The compounds emitted from the surface of the tested samples adsorbed on the fibers were tested under the same conditions as for the standards. The test sample components were then identified using the obtained retention times and use of the Wiley 138 library.

The tested chemical compounds in the volatile phase were collected by divinylbenzene/carboxen/polydimethylsiloxane SPME fibres purchased from Sigma Aldrich. The fibre was placed for 30 min over the sample in the measurement chamber. Then, it was transferred into the GC-MS device. More technical information and procedure steps were described in another publication by the authors [26] and in the Supplementary Materials A (Section 3. Gas chromatography-mass spectrometry (GC-MS) analysis).