Determination of humic acid (HA) and sodium alginate in water using Fe2O3 and CuO nanoparticle-modified glassy carbon electrode

Abstract

ABSTRACT This study reported the determination of humic acid (HA) and sodium alginate (Na-Alg) at glassy carbon electrode (GCE) modified with iron oxide (Fe2O3) and copper oxide (CuO) nanoparticles (NPs), respectively. The synthesised NPs were characterised using spectroscopic and microscopic techniques. Successful modification of the electrode with NPs was confirmed with 1 mM Ferri/Ferro ([Fe(CN)6]3−/4−) redox probe using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Results indicated that GCE-Fe2O3 and GCE-CuO have higher current responses with lower charge transfer resistance (Rct) compared with the bare GCE. Electrocatalytic oxidation of HA and Na-Alg at the modified electrode showed a current drop due to adsorption of the analyte or electrode fouling effect. GCE-CuO showed better resistance to the analyte fouling effect with 17.7% and 31.1% current drops after second scan in HA and Na-Alg, respectively. The limit of detection values were 5.42 μM (HA), 5.06 μM (Na-Alg) at GCE-Fe2O3 electrode and 4.88 μM (HA), 3.82 μM (Na-Alg) at GCE-CuO electrode using LSV technique. The adsorption equilibrium constant β at the electrodes ranged from 3.03 to 60.50 × 104 M−1, while free energy due to adsorption ΔGo ranged from −25.57 to −32.99 kJmol−1. The developed sensors can be used for detection and monitoring of HA and sodium alginate in treated and untreated water samples.