Nanoscale electrochemical sensing of tramadol with a polyoxometalate-modified electrode

Ensuring the accuracy and reliability of analytical methods is essential to ensure the efficacy and safety of pharmaceutical treatments. This study describes a rapid and cost-effective electroanalytical nanosensing platform for tramadol detection, an opioid analgesic widely used in clinical settings but prone to misuse. The sensing material is based on a polyoxometalate, [H 4 PW 17 V ( IV ) O 62 ] 9− (POM), which was successfully synthesized, then characterized by Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) which together allow to confirm its morphology, composition, crystalline structure, and surface chemical states. A glassy carbon electrode (GCE) modified with this POM (POM/GCE) was evaluated by cyclic voltammetry using [Fe(CN) 6 ] 3− and [Ru(NH 3 ) 6 ] 3+ as redox probes, and square wave voltammetry was employed for tramadol detection in aqueous solution. Key experimental parameters including pH, suspension volume, frequency, and accumulation time were optimized to enhance the sensor sensitivity. Under optimal conditions (pH 3, 3 μL modifier, 25 Hz, no accumulation time), the sensor exhibited a linear response from 0.06 to 0.78 μM (R 2 = 0.998), with a detection limit of 4.03 nM and quantification limit of 13.4 nM. The method showed a good reproducibility (RSD 2.2 %) and stability, and was successfully applied to the analysis of pharmaceutical formulations, yielding recovery rates between 97 and 101 %. In comparison to UV–Visible Spectroscopy, the proposed method demonstrated higher sensitivity, a lower detection limit, and improved selectivity for tramadol determination in pharmaceutical formulations. These advantages highlight its potential as a reliable alternative for routine analysis and drug quality control. • Novel voltammetric sensor based on a polyoxometalate-modified glassy carbon electrode for tramadol detection. • High sensitivity with a 4.03 nM detection limit and excellent linearity (R 2 = 0.998). • Cost-effective and rapid method with optimized experimental conditions. • Successful application to pharmaceutical samples, outperforming UV–Vis spectroscopy.