A novel modified electrode based on terbium oxide and carbon nanotubes for the simultaneous determination of methyldopa and paracetamol

Abstract

A novel voltammetric sensing platform was prepared ultrasonically by modifying a glassy carbon electrode (GCE) with a composite of terbium oxide (Tb₄O₇NPs) nanoparticles and carbon nanotubes (CNTs) for the simultaneous determination of methyldopa (MD) and paracetamol (PR). The composite layer was characterized by energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The proposed composite electrode (Tb₄O₇NPs/CNTs/GCE) presented well-defined redox couples for MD and PR, excellent catalytic activities, and large enhancement of the peak current responses compared with bare GCE and CNTs/GCE. The separation of anodic and cathodic peak potentials (ΔE_p) for both MD and PR was only 10 mV indicating that the voltammetric sensor has greatly accelerated the oxidation processes compared to bare GCE and CNTs/GCE. Results also showed that the common interfering molecule ascorbic acid (AA) had no influence on selective determination of MD and PR. Moreover, an internal standard procedure was employed to obtain the heterogeneous rate constant, k⁰, for various electrodes. Square wave voltammetry (SWV) was utilized for simultaneous determination of MD and PR in 0.1 M phosphate buffer solution (PBS) at pH 4.0 at Tb₄O₇NPs/CNTs/GCE. The current responses were linear with concentrations over the range from 5.0 × 10⁻⁹ M to 1.0 × 10⁻⁶ M and 1.0 × 10⁻⁹ M to 9.0 × 10⁻⁷ M for MD and PR, respectively. The detection limits were 1.5 × 10⁻⁹ M and 3.3 × 10⁻¹⁰ M for MD and PR, respectively (based on 3S_b/m). The proposed composite electrode exhibited highly improved voltammetric behaviour, excellent selectivity, high sensitivity, and good reproducibility for MD and PR. The proposed procedure was successfully applied to the analysis of pharmaceuticals and urine samples.