Electrochemical sensing and quantification of theobromine in cocoa products at polyvaline functionalized graphite...

Theobromine (THB), an alkaloid present in various plants, is widely used in pharmaceutical formulations and food products. Increased consumption leads to health risks in both humans and animals.

An electrochemically polymerized polyvaline-modified graphite paste sensor (PVMGPS) was developed in this work to investigate the mechanistic and kinetic pathways of the electrooxidation of THB. Electrochemical impedance spectroscopy and scanning electron microscopy were used for characterizing the designed sensors. The fabricated PVMGPS under optimal conditions produced enhanced current responses compared to the bare graphite paste sensor (BGPS). Multiple parameters were investigated using cyclic voltammetry and differential pulse voltammetry.

The electroactive surface areas of the BGPS and PVMGPS were evaluated as 0.025 and 0.252 cm², respectively. The study of the effect of pH of phosphate buffer solution (PBS) and further analysis revealed that the electro-oxidation involves equivalent numbers of electrons and protons. Scan rate dependence revealed that the oxidation of THB proceeds through diffusion-controlled kinetics. The limit of detection and limit of quantification were evaluated to be 1.22 and 4.08 μM, respectively. Moreover, the voltammetric assay demonstrated a good recovery rate, proving the efficacy of the proposed sensor in detecting THB-containing food samples.

The outcome of the analysis substantiated the efficacy, selectivity and sensitivity of the developed novel sensor for THB detection.