## 4 Conclusions  
In this study, robust and sensitive solid phase microextraction (SPME) coupled with liquid chromatography (LC) and fluorescence/ultraviolet-diode array detection was successfully developed for the determination of quercetin and trans-resveratrol. The optimization of the chromatographic, detection, and SPME extraction/desorption conditions revealed that polyacrylate, polyethylene glycol, and a homemade polydopamine (PDA)-coated fiber exhibited the best performance, with wide linearity ranges (0.03-1 \(\mathrm{\SIUnitSymbolMicro g}\)/mL for quercetin and 0.01-1 \(\mathrm{\SIUnitSymbolMicro g}\)/mL for trans-resveratrol), high sensitivity (LODs of 0.01 \(\mathrm{\SIUnitSymbolMicro g}\)/mL for quercetin and 0.003 \(\mathrm{\SIUnitSymbolMicro g}\)/mL for trans-resveratrol), and good precision. Among these, the polyacrylate coating demonstrated a superior analytical performance and was selected for the analysis \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Fiber**} & \multirow{2}{*}{**Analyte**} & **Range Linearity** & **Equation** & **R2** & **LOD** & **Intra-Day (\(\mu\) = 5)** \\  & & **(ug/mL)** & **(Area vs. \(\mathrm{\SIUnitSymbolMicro g}\)/mL)** & & **(\(\mathrm{\SIUnitSymbolMicro g}\)/mL)** & **(\% RSD)** \\ \hline \multirow{2}{*}{PA} & Q & 0.03–1 & y = 150022 x \(-\) 1095 & 0.9980 & 0.010 & 4.5 \\ \cline{2-6}  & R & 0.01–1 & y = 667322 x \(+\) 18583 & 0.9982 & 0.003 & 3.4 \\ \hline \multirow{2}{*}{PEG} & Q & 0.03–1 & y = 47038 x \(-\) 1025 & 0.9956 & 0.010 & 8.0 \\ \cline{2-6}  & R & 0.01–1 & y = 598123 x \(+\) 20145 & 0.9978 & 0.003 & 9.8 \\ \hline \multirow{2}{*}{PDA} & Q & 0.06–1 & y = 42747 x \(+\) 1356 & 0.9938 & 0.020 & 8.2 \\ \cline{2-6}  & R & 0.01–1 & y = 653660 x \(+\) 2010 & 0.9986 & 0.003 & 9.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Linearity, sensitivity, and precision of the developed SPME-LC- UV-DAD method using the PA, PEG, and PDA fibers. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fiber** & \multicolumn{2}{c}{**Dynamic**} & \multicolumn{2}{c}{**Static**} & \multicolumn{2}{c}{**Carry-Over**} \\ \hline  & **Q** & **R** & **Q** & **R** & **Q** & **R** \\ \hline PDMS/DVB & 1.34 & 0.79 & 0.62 & 0.61 & 36\% & 23\% \\ PEG & 1.68 & 1.27 & 0.62 & 0.61 & 63\% & 52\% \\ PDMS & 0.76 & 0.73 & 0.60 & 0.60 & 19\% & 18\% \\ PA & 0.84 & 0.81 & 0.61 & 0.61 & 27\% & 25\% \\ \hline PDA & 3.33 & 0.81 & 0.61 & 0.61 & 82\% & 25\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(\mathrm{S_{w0.09\mathrm{h}}}\) and carry-over obtained in dynamic and static desorption modes. of winemaking by-products (seeds, skins, and stalks). Quercetin and trans-resveratrol were successfully quantified in pomace extracts at concentrations of 104.3 \(\pm\) 8.2 \(\upmu\)g/g and 38.5 \(\pm\) 4.1 \(\upmu\)g/g, respectively. Recovery experiments confirmed the method's accuracy, with recoveries of 99.1 \(\pm\) 7.4% for quercetin and 98.5 \(\pm\) 9.8% for trans-resveratrol. This method provides a reliable and efficient approach for the analysis of these bioactive compounds in complex matrices, offering potential applications in the food and pharmaceutical industries. Conceptualization: A.M.A. and C.Z. ; methodology: A.M.A., N.D.V., and C.Z. ; validation: A.M.A. and G.M. ; investigation: A.M.A. and G.M. ; resources: A.M.A., N.D.V., and C.Z. ; data curation: A.M.A. ; writing--original draft preparation: A.M.A. and C.Z. ; writing--review and editing: A.M.A. ; supervision: [PERSON]; funding acquisition: A.M.A. and C.Z. All authors have read and agreed to the published version of the manuscript. This research was funded by the project funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3--Call for tender No. 341 of 15 March 2022 of the Italian Ministry of University and Research funded by the European Union--NextGenerationEU; Project code PE00000003, Concession Decree No.