Electroanalytical platforms for codeine determination - A comparison between electrified liquid-liquid interface and glassy carbon electrode.

In this work, we used two common, yet physiochemically different, sensing interfaces to study electrochemical behavior and to provide electroanalytical protocols for codeine (COD) detection. Applied sensing interfaces are the interface between two immiscible electrolytes solutions (ITIES), and the glassy carbon electrode (GCE), which are frequently used for amine-based compounds detection. The electrochemical behavior of COD has been investigated over a broad pH range (2-12) at both ITIES and GCE, with the former yielding important physiochemical parameters, such as formal Galvani ion transfer potential, diffusion coefficients, partition coefficient, distributions constant, and formal Gibbs energy of the ion transfer reaction. Electroanalysis of COD has been performed using classical (macroscopic) and miniaturized (supported with fused silica capillaries) ITIES, the latter providing improved electroanalytical parameters, i.e., lower detection limits (0.75 μM for ITIES vs 6.75 μM for GCE), and significantly increased sensitivity. With the GCE-based system, electrode surface passivation has been encountered, affecting experimental reproducibility and necessitating periodical GCE surface activation. Finally, we have used developed sensing procedures to detect COD in a pharmaceutical formulation, specifically a cough syrup. The performances of all three platforms (macroscopic ITIES, microscopic ITIES (μITIES) and GCE) were compared. The μITIES demonstrated superior electroanalytical properties and displayed the highest recovery rate, thereby highlighting its superiority over GCE in terms of COD determination in real sensing settings.