## 2 Results
### Optimization of HS-SPME on the DVB/CAR/PDMS fiber  
The same DoE used in the investigation of the CW/DVB sorbent, a 2\({}^{2}\) one with three additional replicate experiments in the center of the domain, further expanded with replicate experiments in the points (%NaCl = 10, T = 50 \({}^{\circ}\)C) and (%NaCl = 30, T = 30 \({}^{\circ}\)C), was adopted to model the influence of T and %NaCl on the extraction performance of the DVB/CAR/PDMS fiber. The matrix of the experiments and the experimental and calculated responses are displayed in Table 4. Figure 4, Figure 5, and Figure 6 display the response surfaces and the model coefficients for A\({}_{\text{TOT}}\), A\({}_{\text{ED}}\), and A\({}_{\text{MB}}\), respectively, whereas ANOVA, R\({}^{2}\)adj, and Q\({}^{2}\)adj values are reported in Table  
Figure 4: Optimization of HS-SPME profiling of wine volatiles extracted with the DVB/CAR/PDMS fiber: (**a**) response surface for the total area of the GC chromatogram (\(\text{A}_{\text{TOT}}\)): (**b**) coefficients of the surface model; \(p<0.05\) (*), \(p<0.01\)(**). Figure 5: Optimization of HS-SPME profiling of wine volatiles extracted with the DVB/CAR/PDMS fiber: (**a**) response surface for the peak area of ethyl decanoate (\(\text{A}_{\text{ED}}\)); (**b**) coefficients of the surface model: \(p<0.05\) (*), \(p<0.01\)(**). The response surface of A\({}_{\rm TOT}\) (Figure 4) reveals two maximum conditions, at (%NaCl=10, T = 50 \({}^{\circ}\)C) and (%NaCl=30, T = 30 \({}^{\circ}\)C), although the value of the response in the latter point is slightly higher than the first. On the other hand, A\({}_{\rm TOT}\) values in the other DOE points exhibit small differences, comparable with the fluctuations observed in the replicate experiments. The qualitative trend of A\({}_{\rm ED}\) within the experimental domain (Figure 5) closely reflects that of A\({}_{\rm TOT}\), although it covers a lower variation range than A\({}_{\rm TOT}\). It can be also noted that, different from A\({}_{\rm TOT}\), the maximum in the peak area of ED can be found at the minimum level for %NaCl and at the highest T value. It follows that a T increase and a %NaCl decrease result in the increase of the relative contribution of the peak area of ED to the total area of the chromatogram, which agrees with the behavior of ED in SPME conducted with PDMS and CW/DVB fibers, as discussed in the previous sections. The dependence of A\({}_{\rm MB}\) from T and %NaCl is accurately described by a slightly skewed plane (Figure 6) similar to the surface response observed under the application of PDMS fiber (Figure 3). Furthermore, in this case, despite the variation of this response within the experimental domain being relatively low, the extraction of MB can be enhanced at %NaCl = 30 and T = 50 \({}^{\circ}\)C. The same condition was also found as the optimal for the extraction of MB with the CW/DVB fiber. Therefore, whatever the sorbent is, the increase in volatility and salting out, respectively promoted by T and %NaCl rising, improve the MB extraction. On the other hand, the two almost equivalent maximum conditions for A\({}_{\rm TOT}\) and A\({}_{\rm ED}\) seem to be originated by antagonist T and %NaCl effects combined with the strong interaction of these two factors. To investigate the influence of the SPME conditions on the volatile profile determined by HS-SPME/GC-MS in more detail, PCA was performed on all the peak areas identified in the chromatograms collected in the various DoE points. Before, each peak area was divided by A\({}_{\rm TOT}\) and auto-scaling was applied to the normalized quantities with the scope of exiting the role of variables with low variance. Figure 7 displays the DoE points projected onto the plane of the first two principal components (PC1 and PC2, accounting for about 62 and 13% of the total variance, respectively) together with the variable loadings.