<p>An electrochemical sensor based on carbon black Super P-modified glassy carbon electrode was developed for the determination of total quercetin and methylated derivatives in Dizygostemon riparius extracts. Total quercetin encompasses all quercetin released from glycosidic conjugates after acid hydrolysis, including free quercetin and methylated forms such as 3-O-methylquercetin. The modified electrode was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Comparative studies demonstrated enhanced electrochemical performance of the modified sensor relative to bare glassy carbon electrode, exhibiting improved charge transfer kinetics and increased anodic peak currents for quercetin oxidation. Analytical parameters were optimized using square wave voltammetry, yielding wide linear concentration ranges of 5.0–100 µmol L^-1 for quercetin and 2.5–12.5 µmol L^-1 for 3-O-methylquercetin, with detection limits of 0.06 and 0.041 µmol L^-1, respectively. The sensor exhibited satisfactory selectivity, repeatability (relative standard deviation 1.67%), and reproducibility (relative standard deviation 4.48%). The validated method was successfully applied to quantify total quercetin content in white and lilac morphotypes of Dizygostemon riparius hydroalcoholic extracts following acid hydrolysis, with recovery percentages ranging from 94 to 106% and 98–102%, respectively. Results obtained by the electrochemical method showed good agreement with ultraviolet-visible spectrophotometric analysis. This simple, cost-effective, and reliable electrochemical approach demonstrated significant potential for routine analysis of quercetin derivatives in natural products.</p> Graphical Abstract <p></p>