Electrochemical Oxidation of Flavonoids at a Nano- Metal Oxide Modified Carbon Paste Electrodes and Determination Their Levels in Human Urine

We constructed nano-metal oxide (tin oxide, cerium oxide, cobalt oxide, iron oxide, nickel oxide, gold oxide, and silver oxide) -modified carbon paste electrodes (CPEs) for detecting flavonols (kaempferol, myricetin, and quercetin) and flavones (luteolin and apigenin) using high-performance liquid chromatography with an electrochemical detector (HPLC-ECD). Flavonoids are more efficiently catalytically oxidized on a gold oxid e-modified CPE than on a bare CPE. For direct current mode, with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 40 to 1600 ng mL-1 was found. The limits of quantification for flavonoids were below 0.5 ng. The developed method detected flavonoids in urine samples. Findings using HPLC-ECD and HPLC with an ultraviolet detector were comparable.