# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 2 Materials and Methods
### Gas-Chromatography-Mass Spectrometry  
Solid phase microextraction (SPME) gas-chromatography-mass spectrometry (GC-MS) was used to analyse the volatile compounds of the spirits. Then, 2.5 mL of the spirit were filled into 10 mL magnetic screw cap vials (Gerstel, Muhlheim an der Ruhr, Germany) and adjusted to 20% ABV with the addition of 7.5 mL of a water-ethanol mixture. Then, 50 mL of methyl-heptanoate (Sigma-Aldrich, St. Louis, MO, USA) at a concentration of 22 ppm was added as an internal standard to each spirit. Spirits were prepared at least 24 h prior to analysis.  
A Trace GC with Finnigan Trace MS from ThermoQuest (Waltham, MA, USA), with a PAL system (CTC Analtyics, Zwingen, Switzerland) coupled to a Multi-Purpose Sampler MPS2-Twister autosampler (Gerstel, Muhlheim an der Ruhr, Germany) with a DB WAX-UI column 60 m, 0,32 mm, 0.50 m (Agilent, Santa Clara, CA, USA) was used to analyse the spirits.  
Spirits were incubated for 10 min at 35 \({}^{\circ}\)C. A DVB/CAR/PDMS 50/30 \(\upmu\)m fibre (Supelco Inc., Bellefonte, PA, USA) was used to extract the volatiles and injected splitless to the column with an injector temperature of 250 \({}^{\circ}\)C, a split flow of 40 mL/min and a splitless time of 1 min. The temperature program of the oven was 2 min at 35 \({}^{\circ}\)C with a rate of 5 \({}^{\circ}\)C/min to 250 \({}^{\circ}\)C and holding this temperature for an additional 10 min with a flow rate of 1.4 mL/min. Four independent samples were taken from each spirit, these were measured in duplicate, giving a total of eight measurements per spirit. A full scan was done with a solvent delay of 1 min. \(m/z\) between 35 and 350 were scanned. Peaks were included where the minimum peak height of 3.0 signal to noise was exceeded and the mass spectra could be identified by the used library NIST Mass Spectral Sear Program and NIST/EPA/NIH Mass Spectral Library Version 1.7 (National Institute of Standards and Technology, Gaithersburg, MD, USA). Xcalibur software (Home page version 1.2, ThermoScientific, Waltham, MA, USA) was used to analyse the data.  
Peak areas were determined for each compound and semi-quantitatively analysed: peak areas were measured and compared, but no standards and calibration lines were created. Compounds were assigned to groups based on both chemical structure and flavour. Flavour groupings were assigned based on the compound flavour descriptions given on the Good Sents Company website [[http://www.thegoodscentscompany.com/](http://www.thegoodscentscompany.com/)]([http://www.thegoodscentscompany.com/](http://www.thegoodscentscompany.com/)) accessed on 29 January 2021. The compounds were then grouped according to the flavour attributes used in the QDA evaluation described in Section 2.2.3. Compounds without listed descriptors (no aroma or not listed) were assigned as _not described_.  
PCA based on correlation was used to summarise the data and produce a product map. This was carried out using RStudio Version 1.3.103 (RStudio PBC, Boston, MA, USA) and the packages FactoMineR and ggplot2. The first two dimensions of this analysis are presented in this paper.