Electrocatalytically Active Hierarchical CuO Microspheres for Simultaneous Voltammetric Determination of Theophylline and Terbutaline Sulfate

This work reports an electrochemical sensor constructed by incorporating hierarchical CuO microspheres into a carbon paste electrode (H-CuO-MS-CPE) for the simultaneous voltammetric detection of theophylline (TP) and terbutaline sulfate (TBS). The hierarchical CuO microspheres exhibit enhanced electrocatalytic activity, offering abundant active sites, a large electroactive surface area, and accelerated electron-transfer kinetics, which collectively improve the intrinsic electrochemical performance of the electrode. Consequently, the sensor promotes efficient adsorption and oxidation of TP and TBS, thereby improving both sensitivity and selectivity. The sensor produced two well-separated oxidation peaks corresponding to TP and TBS that demonstrate its ability to distinguish between the analytes. Using adsorptive stripping differential pulse voltammetry (AdSDPV), the detection limits for simultaneous determination were 0.047 μM for TP (linear range: 0.25–237 μM) and 0.066 μM for TBS (linear range: 0.42–362 μM). Furthermore, the sensor demonstrates excellent stability, selectivity, and resistance to common interferences, including K + , Na + , Ca 2+ , Mg 2+ , Cl − , NO 3 − , SO 4 2− , NH 4 + , glucose, uric acid, dopamine, lactate, and ascorbic acid. In addition, the sensor shows good repeatability and reproducibility, with %RSD values remaining below 5%. The developed sensor was successfully applied to detect TP and TBS in pharmaceutical formulations and biological samples (blood and urine) with minimal interference effects.