<p>A novel electrochemical sensing platform based on a Mn_0.5Zn_0.5Fe₂O₄ nanoparticles-modified carbon paste electrode (MnZnFe NPs/CPE) was developed for the simultaneous voltammetric determination of trace Cd²⁺ and Pb²⁺ ions. MnZnFe NPs were synthesized via co-precipitation method and characterized by FTIR, XRD, SEM&amp;EDX, and TEM analyses, confirming the formation of a well-crystallized spinel ferrite structure with nanoscale morphology. The incorporation of MnZnFe NPs significantly enhanced the electrocatalytic activity of the carbon paste matrix, providing improved adsorption capacity and electron-transfer kinetics for metal ions. Adsorptive stripping differential pulse voltammetry (ASDPV) was employed for analytical measurements under optimized conditions (pH 5, deposition potential − 1.2&#xa0;V, deposition time 120&#xa0;s). The modified electrode exhibited well-defined and separated oxidation peaks for both Cd²⁺ and Pb²⁺, achieving low detection limits 0.21 nM and 0.03 nM for Cd²⁺ and Pb²⁺ respectively, wide linear ranges 0.80 nM – 28.0 µM and 0.12 nM– 30.0 µM for Cd²⁺ and Pb²⁺ respectively, and excellent reproducibility (RSDs of 0.42% (Cd²⁺) and 1.39% (Pb²⁺)). The sensor also demonstrated high selectivity toward Cd²⁺ and Pb²⁺, with negligible interference from common coexisting ions, and showed good stability over repeated use. The developed MnZnFe NPs/CPE provides a simple, low-cost, and efficient approach for monitoring toxic heavy metals in environmental water samples.</p>