Fabricating a new electrochemically modified pencil graphite electrode based on acetophenone (2,4-dinitrophenyl)hydrazone for determining selenium in food and water samples

Determination of selenium compounds in air, soil, water, and food samples is of interest as selenium's bioavailability and toxicity depend on its concentration level. Among analytical approaches, electrochemical sensors are more favorable due to their simplicity, time-saving, cost-effectiveness, and high sensitivity. In this study, we report electrochemical determination and analysis of selenium at the surface of a pencil graphite electrode modified with a sensing composite film composed of acetophenone (2,4-dinitrophenyl)hydrazone, polypyrrole, and copper nanoparticles. To produce durable films, cyclic voltammetry technique, as a facile modification procedure, was used. The electrochemical response of the fabricated modified electrode to selenium was evaluated using cyclic and square wave voltammetry techniques. The modified electrode presented excellent electrocatalytic ability with favorable electrochemical parameters (α = 0.24, log ks = 3.27 s−1, and Γ = 3.74 × 10−7 mmol cm−2) for the reduction of selenium in acidic media with optimized pH of 2 and working potential of around −0.85 V (vs. SCE). The scanning electron microscopy images of the modified surfaces proved the formation of aggregates in nanoscale, indicating successful electrodeposition and electro-polymerization processes to modify the pencil graphite surface. This revealed a linear electrochemical response to selenium within the concentration range from 50 nM to 110 nM with the limit of detection (LOD) of 16.58 nM. The analytical application of the new sensor was also examined with respect to its applicability in food samples, such as milk, and water samples, including food wastewater samples, suggesting valid determination of selenium without any side interference.