Electrochemical Behavior of Cu(II) on Carbon Paste Electrode Modified by Humic Acid, Cyclic Voltammetry Study

Polarography at dropping mercury electrode and infrared spectroscopy were used to confirm the reaction of copper(II) ions with humic acid in solution. Polarography allowed observing the reaction to follow the concentration of the Cu(II) in solution while infrared permitted one to follow the humic acid complexation. Cyclic voltammetry experiments, at stationary carbon paste electrode, showed original properties of humic acid which adsorbs at the surface of carbon paste electrode that becomes appropriate for the preconcentration and identification of Cu(II) species. Although very promising the use of adsorption showed the disadvantage of not being reproducible therefore we developed a new preparation method for the carbon paste electrodes modified with humic acid that allow highly repeatable measurements. Humic acid was dissolved in base solution before mixing it with carbon graphite powder and freeze-drying to lead to a fine powder that allows reproducible batches of electrodes. The modification of carbon paste electrode with two different humic acids revealed that the electrochemical behavior of Cu(II) solutions depends on the nature of the humic material. The effects on the electrochemical behavior of Cu(II) of the solutions pH and the ratio of humic acid in the bulk of the electrode were also examined. Such carbon paste electrodes modified with humic acid extracted from a peat area in the Mogi Guaçu River at Sao Paulo State in Brazil showed high reproducibility and particular stability in solution (pH range of 3.0 to 5.5) entitling them to be very good candidates for analytical purposes.