## 2 Results
### Optimization of Solid-Phase Microextraction (SPME) Parameters
#### 2.1.2 Effect of Ethanol and Sodium Chloride Concentration  
In the next step of the experiments, the concentration of ethanol as well as addition of NaCl to the samples were evaluated. Three levels of ethanol content (% _v/v_) and four of NaCl dose (% _w/v_) in samples was analyzed, respectively, 2.5, 5, and 10, and 0, 10, 20, and 30. The results are displayed in Table 1. It is clear that with the increasing ethanol content in the samples, the area of peaks decreased, especially for thiols (1-propanethiol, 1-butanethiol, 1-pentanethiol). The less sensitive to the increasing ethanol content were dibutyl sulfide and dipropyl sulfide. The influence of the ethanol content in samples has been investigated to determine the extent to which the extraction is disturbed by higher alcoholic strength of the solution. This is particularly important when spirit beverages are to be analyzed, as the reduction of alcohol concentration is inextricably linked to the dilution of the remaining analytes present in the sample, including VSCs. Figure 1: The results of SPME/GC–MS analysis of different fiber coatings (SPME extraction at 50 \({}^{\circ}\)C for 15 min). PDMS—100 μm Polydimethylsiloxane, PEG—60 μm Carbowax/Polyethylene Glycol, PA—85 μm Polyacrylate, CAR/PDMS—85 μm Carboxen/PDMS, Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS)—50/30 μm DVB/Carboxen/PDMS. Bars represents the peak area and dots represents number of detected peaks. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{2}{c}{**Ethanol**} & \multicolumn{2}{c}{**2.5\%**} & \multicolumn{4}{c}{**5\%**} & \multicolumn{4}{c}{**10\%**} \\ \cline{2-13}  & **NaCl** & **0** & **10** & **20** & **30** & **0** & **10** & **20** & **30** & **0** & **10** & **20** & **30** \\ \hline Ehhanethiol & 12.3 & 14.5 & 100.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 \\ Dimethyl-sulfide & 25.7 & 28.7 & 100.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 \\
1-Propanethi & 65.2 & 43.1 & 100.0 & 99.5 & 17.7 & 22.6 & 13.9 & 10.9 & 10.4 & 5.7 & 6.3 & 3.8 \\ Thiophene & 71.8 & 55.6 & 100.0 & 64.7 & 18.0 & 42.8 & 54.2 & 28.8 & 13.4 & 22.0 & 27.7 & 14.3 \\ Diethyl-sulfide & 58.9 & 48.0 & 100.0 & 76.0 & 14.2 & 38.2 & 50.5 & 26.5 & 19.1 & 19.4 & 16.6 & 11.9 \\
1-Butanethiol & 80.2 & 53.5 & 100.0 & 74.8 & 22.0 & 32.2 & 48.5 & 25.4 & 30.6 & 19.4 & 22.3 & 11.7 \\ Dimethyl-disulfide & 56.0 & 50.1 & 100.0 & 81.5 & 15.4 & 37.0 & 69.8 & 46.7 & 18.7 & 52.5 & 18.5 & 16.4 \\ Ethyl-thioacetate & 49.9 & 50.8 & 100.0 & 91.3 & 15.0 & 32.7 & 51.6 & 53.9 & 15.2 & 28.6 & 30.7 & 38.4 \\
1-Pentanethiol & 85.2 & 68.3 & 100.0 & 71.1 & 39.0 & 34.5 & 48.9 & 40.9 & 38.9 & 38.4 & 43.9 & 25.3 \\  
The ethanol content is one of the most important parameters to consider when sulfur compounds are extracted from fermented beverages. Recent studies conducted by [PERSON] and [PERSON] (2018) showed that a sharp decrease in detectability of VSCs occurs when ethanol is present in the sample even at 0.5% _v/v_ concentration. The authors also concluded that the alcoholic strength of the tested sample should be between 2%-4% _v/v_ of ethanol to obtain reliable results. Additionally, [PERSON] et al. (2017), when studying VSCs in beer, wine, and whisky, stated that the lowest detection limits can be obtained when the sample:water ratio is 5:15 and 2:18, respectively, for wine and whisky, which corresponds to the ethanol concentration of approximately 5% _v/v_ (similar to that in beer). The addition of sodium chloride to the samples is performed to increase the ionic strength of analytes and enhance the recovery rate due to the \"salting-out\" effect ([PERSON], 2018). The literature gives conflicting information about whether this is a favorable stage or not for SPME, e.g., [PERSON] et al. (2017) stated that the presence of sodium chloride in the amount of 0-1.5 g/5 mL of beer sample did not enhance the extraction of VSCs.