*4.2. Gas Chromatography-Mass Spectrometry Analysis*

Three samples of peppermint EO were analysed by a gas chromatography/mass spectrometry (GC/MS) for qualitative properties in laboratory at University of Prešov. GC/MS analyses were carried out on devices Varian 450-GC and 220-MS. Separation was conducted on a capillary column BR 5ms (30 m × 0.25 mm ID, 0.25 μm film thickness). Injector type 1177 was heated to a temperature of 220 ◦C. Injection mode was splitless (1 μL of a 1:1000 n-hexane solution). Helium was used as a carrier gas at a constant column flow rate of 1.2 mL min−1. Column temperature was programmed as follows: initial temperature was 50 ◦C for 10 min, then increased to 100 ◦C for 3 min, maintained isothermally for 5 min and then increased to 150 ◦C for last 10 min. The total time for analysis was 46.67 min. The MS trap was heated to 200 ◦C, manifold 50 ◦C and transfer line 270 ◦C. Mass spectra were scanned every 1 s in the range 40–650 *m*/*z*. The retention indices were determined in relation to the Rt values of a homologous series of n-alkanes (C10–C35) under the same operation conditions. Constituents were identified by comparison of their retention indices (RI) with published data in different literature. Further identification was made by comparison of the mass spectra with those stored either in NIST 02 library or with those from the literature [39]. Components relative concentrations were obtained by percentage of peak area normalization.
