2.4. Gas Chromatography Olfactometry (GCO) Method

The equipment for the analysis of the samples is located in a dedicated laboratory with temperature control where trained panelists could sniff free of distraction. For every session, a diluted new make spirit sample of 5 mL (20%ABV) was added to a 20 mL amber La-Pha-Pack headspace screw capped vial with a magnetic cap and silicone/polytetrafluoroethylene septa (Apex Scientific, Maynooth, Co. Kildare, W23 R1H2, Ireland). A Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) solid phase micro-extraction (SPME) fiber (Agilent Technologies Ireland Ltd., Cork, T45 YX04, Ireland) in an MPS Gerstal autosampler (Anatune Ltd., Cambridge, UK) was exposed to the headspace above the sample at 40 °C for 40 min with agitation using the heater/agitator module. Analyses were performed on an Agilent 7890 Gas Chromatography System using a DB-624UI mid-polar column (20 m × 0.18 mm × 1.0 µm, Agilent Technologies Ireland Ltd, Ireland.) equipped with an Agilent 5975C inert XL mass selective detector (MSD), a flame ionisation detector (FID) and a Gerstal Olfactory Detection Port (ODP 3) (Anatune Ltd., Cambridge, CB3 0GP, UK). The carrier gas was helium, held at a constant flow of 1.2 mL/min, and a 3-way splitter was used to split the flow proportionally (1:1:1) from the analytical column to the three detectors (MSD, FID and ODP 3. The transfer lines (deactivated silica capillary tubing) from the splitter were measured between the MSD (3.3 m × 0.15 mm), FID (2.14 m × 0.15 mm), and the ODP3 (2.14 m × 0.15 mm) to ensure peak alignment. The total GC run time was 29 min. The initial oven temperature was 40 °C for 2 min, raised to 140 °C at 6 °C/min, and finally to 220 °C at 15 °C/min and held for 5 min. Detection was performed in full scan mode with the mass range between 35 and 250 amu. All samples were analysed in triplicate. Sniffing was carried out in a temperature controlled room (21 °C), and humidified nitrogen was added to the transfer line to prevent nasal mucosa dehydration. The compounds were identified by olfactory descriptions, reference analytical standards, and/or mass spectra comparison to the NIST 2014 mass spectral library and their linear retention indices (LRI) were calculated using homologous series of C5–C20 n-alkanes.