## 2 Results and Discussion
### Optimisation of SPME Extraction Conditions
There is also no evidence of lack of fit in the model. By studying Table S1, one can see that the most significant terms are extraction temperature and extraction time. The interaction between desorption temperature and desorption time also appears to be of significance. A contour plot for the response surface of extraction time and extraction temperature can be seen in Figure 2. The plot indicates that the optimal point for these two factors is close to their maximum values. It also indicates that extraction time matters less as extraction temperature increases and vice-versa. For example, at a temperature of 85 \({}^{\circ}\)C, the same effect is achieved with an extraction time between 40 and 65 min. However, the initial screening study indicated that at temperatures above 55 \({}^{\circ}\)C an increase in oxidation products is witnessed. Therefore, a safer factor level selection would be an extraction temperature of 55 \({}^{\circ}\)C and an extraction time of 50 min. As the interaction between desorption time and desorption temperature appears significant, by studying their contour plot at Figure S1 at the selected extraction time and temperature, one can see a saddle-like plot, which suggests that optima lie with one factor maxed or the other. To keep desorption temperature as low as possible to avoid any oxidation or thermal degradation effects at the inlet, a selection of desorption temperature of 240 \({}^{\circ}\)C and desorption time of 12 min is made. Regarding conditioning time, all the models' terms for this factor appear not to be significant, so a choice of the shortest time is made, in this case 5 min. In summary, the SPME conditions chosen for analysis are 55 \({}^{\circ}\)C of extraction temperature, 5 min of conditioning time, 50 min of extraction time, and 240 \({}^{\circ}\)C and 12 min desorption temperature and time, respectively. The aim of the present study was the development of a method for the comprehensive profiling of the volatile content of VOOs. The oven program seemed to be appropriate for the most volatile components, since at 17 min and 180 \({}^{\circ}\)C all components of interest were eluted. The DVB/CAR/PDMS fiber showed high extraction efficiency and was selected for further study. Extraction temperature and extraction time had a great effect on the detection of volatile components and their composition. With an extraction temperature of 55 \({}^{\circ}\)C and an extraction time of 50 min, an increased area of the total ion chromatogram was \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Multiple R-Squared** & \multicolumn{2}{c}{0.9028} & & & \\ \hline
**Adjusted R-Squared** & \multicolumn{2}{c}{0.7262} & & & \\
**\(p\)-Value** & \multicolumn{2}{c}{4.02 \(\times\) 10\({}^{-3}\)} & & & & \\ \hline  & **Df** & **Sum Sq** & **Mean Sq** & **\(F\) Value** & **Pr (\textgreater{}F)** \\ \hline FO (x1, x2, x3, x4, x5) & 5 & 1.2055 \(\times\) 10\({}^{18}\) & 2.4111 \(\times\) 10\({}^{17}\) & 16.3748 & 9.02 \(\times\) 10\({}^{-5}\) \\
**TWI (x1, x2, x3, x4, x5)** & 10 & 1.9382 \(\times\) 10\({}^{17}\) & 1.9382 \(\times\) 10\({}^{16}\) & 1.3164 & 0.3283 \\
**PQ (x1, x2, x3, x4, x5)** & 5 & 1.0584 \(\times\) 10\({}^{17}\) & 2.1168 \(\times\) 10\({}^{16}\) & 1.4376 & 0.2855 \\
**Residuals** & 11 & 1.6197 \(\times\) 10\({}^{17}\) & 1.4724 \(\times\) 10\({}^{16}\) & & \\
**Lack of Fit** & 6 & 4.5182 \(\times\) 10\({}^{16}\) & 7.5303 \(\times\) 10\({}^{15}\) & 0.3224 & 0.8996 \\
**Pure Error** & 5 & 1.1679 \(\times\) 10\({}^{17}\) & 2.3357 \(\times\) 10\({}^{16}\) & & \\ \hline \hline \end{tabular}  
FO stands for First Order terms, TWI for Two Way Interaction terms and PQ for Pure Quadratic terms. Df are the Degrees of Freedom, Sum Sq the Sum of Squares and Mean Sq the Mean Square. Extraction temperature (x1), conditioning time (x2), extraction time (x3), desorption time (x4) and desorption temperature (x5).  
\end{table} 
Table 1: Model fit data along with corresponding output from the ANOVA analysis table.