Simultaneous Determination of Quercetin and Trans-Resveratrol in Winemaking Waste by Solid Phase Microextraction Coupled to High-Performance Liquid Chromatography with Fluorescence and Ultraviolet Detection

A solid phase microextraction (SPME) method coupled with liquid chromatography (LC) and fluorescence/ultraviolet-diode array detection was developed for the simultaneous determination of quercetin and trans-resveratrol. The chromatographic, detection, and SPME extraction/desorption conditions were systematically optimized. The performance of four commercial SPME fibers—polyacrylate (PA), polyethylene glycol (PEG), polydimethylsiloxane (PDMS), and polydimethylsiloxane-divinylbenzene (PDMS-DVB)—was evaluated and compared with a homemade polydopamine (PDA)-coated fiber. While all of the fibers successfully extracted the target analytes, their efficiencies varied significantly. The PA, PEG, and PDA fibers demonstrated superior performance, exhibiting wide linearity ranges (0.03–1 µg/mL (PA and PEG) and 0.06–1 µg/mL (PDA) for quercetin, 0.01–1 µg/mL for trans-resveratrol); high sensitivity (LODs of 0.01 µg/mL (PA and PEG) and 0.02 µg/mL (PDA) for quercetin, 0.003 µg/mL for trans-resveratrol); and excellent precision. Among these, the polyacrylate coating delivered the best analytical performance and was selected for further application. The optimized method was applied to analyze winemaking by-products (seeds, skins, and stalks) using SPME on ethanol-macerated extracts subjected to brief ultrasonication. Quercetin and trans-resveratrol were quantified in pomace extracts at concentrations of 104.3 ± 8.2 µg/g and 38.5 ± 4.1 µg/g, respectively. Recovery experiments confirmed the method’s accuracy, with recoveries of 99.1 ± 7.4% for quercetin and 98.5 ± 9.8% for trans-resveratrol. This study establishes a reliable, sensitive, and efficient approach for the determination of these bioactive compounds in complex matrices, with potential applications in the food and pharmaceutical industries.