## 2 Materials and Methods
### GC-MS and GC\(\times\)GC-TOF-MS Analysis of Volatile Arona Compounds  
The two techniques/methods used (HS-SPME with 1D-GC-MS and GC\(\times\)GC-TOF-MS, respectively) were validated and used with different setups in two different laboratories, one in Croatia [29] and another in Italy [22; 30; 31], respectively. The methods were tested many times with papers published from both sides based on the obtained results; therefore, the obviously different method/instrumentation setups were considered appropriate for the purpose, and at the same time complementary. The intention was not to confront the two techniques, but to obtain as much information as possible by combining the two \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Physico-Chemical Parameter**} & \multicolumn{2}{c}{**Variety**} \\ \cline{2-3}  & **PM** & **TE** \\ \hline Specific gravity 20 \({}^{\circ}\)C/20 \({}^{\circ}\)C & 0.9944 \(\pm\) 0.0016 & 0.9950 \(\pm\) 0.0010 \\ Alcoholic strength (vol. \%) & 14.2 \(\pm\) 0.5 \({}^{\mathrm{a}}\) & 13.0 \(\pm\) 0.9 \({}^{\mathrm{b}}\) \\ Total acidity (as mg/L tartaric acid) & 5.3 \(\pm\) 0.3 & 6.7 \(\pm\) 1.8 \\ Volatile acidity (as mg/L acetic acid) & 0.27 \(\pm\) 0.08 & 0.35 \(\pm\) 0.09 \\ Total dry extract without reducing sugars (g/L) & 29.9 \(\pm\) 3.7 & 29.0 \(\pm\) 3.8 \\ pH & 3.63 \(\pm\) 0.12 & 3.44 \(\pm\) 0.28 \\ \hline \hline \end{tabular} Varieties: PM—Plavac mali, TE—Teran. Different superscript lowercase letters in a row represent statistically significant differences between mean values at \(p<\) 0.05 obtained by one-way ANOVA and [PERSON]’s least significant difference (LSD) test.  
\end{table} 
Table 1: Physico-chemical parameters in Plavac mali and Téran monovarietal red wines. approaches, and to investigate how much benefit the GC\(\times\)GC-TOF-MS technique/method can bring into research on wine varietal differentiation. Prior to analysis by GC-MS, volatile aroma compounds were extracted using HS-SPME as proposed by [PERSON] et al. [29] with slight modifications. Wine samples were four times diluted with deionized water and put in a 10 mL glass vial containing 1 g of ammonium sulfate. A 50 \(\upmu\)L aliquot of internal standards solution (2-ocanol at 0.84 mg/L, 1-nonanol at 0.82 mg/L, and heptanoic acid at 2.57 mg/L) was added. A DVB-CAR-PDMS SPME fiber was preconditioned above the sample for 15 min at 40 \({}^{\circ}\)C and then subjected to the vapors in the headspace for 40 min at 40 \({}^{\circ}\)C with stirring (800 rpm). Volatile compounds were desorbed in a GC-MS injector at 248 \({}^{\circ}\)C for 10 min (3 min splitless mode). GC-MS identification and quantification was performed using a Varian 3900 gas chromatograph (GC) connected to a Varian Saturn 2100T mass spectrometer with an ion trap analyzer (Varian Inc., Harbour City, CA, USA). The GC was equipped with a 60 m \(\times\) 0.25 mm i.d. \(\times\) 0.25 \(\upmu\)m d.f. capillary column Rtx-WAX (Restek, Belafonte, PA, USA). The GC column was initially heated at 40 \({}^{\circ}\)C, the temperature was then increased at 2 \({}^{\circ}\)C/min to 240 \({}^{\circ}\)C, and then kept constant for the final 10 min. The carrier gas was helium at a flow rate of 1.2 mL/min. EI mode (70 eV) was used to acquire mass spectra in the 30-350 \(m/z\) range. Volatile compounds were identified by comparison of their retention times and mass spectra with those of pure standards and with mass spectra from NIST05 library. A spectra reverse match number (RM) higher than 800 was used as a criterion, whereas in particular cases for spectra with RM < 800 the identification was performed based on the satisfactory ratio of relative intensities of a quantifier ion and next three characteristic ions with the highest intensity. Additional confirmation of the identity of compounds was achieved by comparing linear retention indices calculated relative to the retention times of C\({}_{10}\) to C\({}_{28}\) n-alkanes to those reported in literature obtained using equal or equivalent capillary columns.