Cerium-Dioxide-Nanoparticle-Modified Electrode for Voltammetric Determination of Propyl Gallate

Abstract

A novel glassy carbon electrode modified with cerium dioxide (CeO₂) nanoparticles and hexadecylpyridinium bromide is developed for the voltammetric determination of propyl gallate. The hexadecylpyridinium acts as a dispersing agent that stabilized the nanomaterial and as a co-modifier of the electrode surface. Modification of the glassy carbon electrode lowered the propyl gallate oxidation peak potential by 20 mV and provided a 2.6-fold increase in the oxidation peak current. The bare and modified glassy carbon electrodes are characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. A statistically significant increase in the effective surface area of the modified electrode is shown (32.4 ± 0.5 mm² as compared with 8.9 ± 0.3 mm² for the bare glassy carbon electrode). The electrochemical impedance data indicate a 2100-fold decrease in the charge transfer resistance as compared to the bare glassy carbon electrode, which confirms the increase in the electron transfer rate (k_et = 1.13 × 10^–5 and 2.42 × 10^–2 cm/s for glassy carbon electrode and CeO₂-nanoparticles/glassy carbon electrode, respectively). Propyl gallate electrooxidation occurred irreversibly with the participation of protons and is controlled by surface processes. The parameters of electrooxidation are calculated and a scheme of the electrode reaction is suggested. The linear dynamic ranges of propyl gallate in the differential pulse voltammetry are 0.10–2.5 and 2.5–50 μM, with a detection limit of 0.022 μM. The selectivity of the electrode response to propyl gallate in the presence of inorganic ions and carbohydrates is demonstrated. Since the propyl gallate is used to prevent oxidation of vegetable oils, α-tocopherol and other antioxidant additives (tert-butylhydroxyanisole and tert-butylhydroxytoluene) used together with propyl gallate are considered as potential interfering agents. A 5-fold excess of α-tocopherol, a 10-fold excess of tert-butylhydroxyanisole and equimolar amounts of tert-butylhydroxytoluene do not interfere with the propyl gallate determination. The method is tested on extracts of sunflower and sesame oils.