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Using eco-friendly, cheap, and available adsorbents is promising for the determination of metal ions. So, this study focuses on the modification of graphite reinforcement carbon paste electrode (GRCPE) with mango seed kernel (MSK) for voltammetric determination of Cd(II). Moreover, to increase the surface area of this adsorbent, it was prepared in nanosized that formed nanoparticles of mango seed kernel (MSK-NPs). The developed nanocomposite electrode of carbon paste electrode modified with nanoparticles of mango seed kernel (MSK-NPs@GRCPE) was characterized using Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). The effect of pH, buffer solution, and supporting electrolyte as experimental conditions were optimized through differential pulse adsorptive anodic stripping voltammetric method (DPAdASV). Britton-Robinson buffer pH = 3.9 at Eacc = – 1400 mV, tacc = 30 s, pulse width = 10 ms and sampling time = 8 ms were the optimum conditions for determination of Cd(II). The LOD and LOQ of MSK-NPs@GRCPE were calculated at 5.44 × 10–9 and 1.65 × 10–8 M, respectively. Compared with bare graphite reinforcement carbon paste electrode (BGRCPE), the nanocomposite MSK-NPs@GRCPE has a lower detection limit, indicating that the presence of MSK-NPs could greatly improve the response to Cd(II). The practical applicability of the electrode was verified by the determination of Cd(II) in chocolate and white rice samples. The results show high selectivity and sensitivity for Cd(II) in real samples. Graphical abstract

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In this work, silica fume (SF) is used as a solidphase extractor for extraction of Zn(II) and Cd(II) from aqueous solutions. Characterization of SF is performed by Fourier transform infrared, X-ray diffraction, transmission and scanning electron microscopy. The optimum experimental conditions for the two metal ions are investigated using batch and column techniques. The maximum adsorption capacity values are found to be 54.13 and 121.28 mg g -1 at the optimum pH 6.0 and 8.0 for Zn(II) and Cd(II), respectively. The equilibrium data are analyzed using the Langmuir, Freundlich, and Temkin isotherms by nonlinear regression analysis. Also, the kinetics analysis revealed that the overall adsorption process is successfully fitted with the pseudo-second-order model. The method is applied for determination of the target metal ions in pharmaceutical and environmental samples using squarewave anodic stripping voltammetry. The limit of detection (LOD) values are 0.102 and 1.43 9 10 -3 mg L -1 for Zn(II) and Cd(II), respectively. The percentage recovery values are 98.8-100.5 % which indicate the success of the proposed method for determination of Zn(II) and Cd(II) without interfering effects.