Flow injection analysis-stripping voltammetric sensor for determination lead(II) in aqueous environments

This study reports the fabrication and analytical performance of a multi-walled carbon nanotube paste electrode modified with ferrocenium tetrachlorobismuthate (FTB@MWCNTs/CPE) for the voltammetric detection of lead ions (Pb²⁺) in aquatic environments. The modified composite was characterized using Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) to confirm its morphological and structural features. The electrochemical behavior of the redox-active FTB modifier was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry, revealing improved electron transfer properties as evidenced by the decrease in charge transfer resistance and the increase in electroactive surface area at an optimal FTB loading of 10% (w/w). Square wave stripping voltammetry (SWSV) coupled with a flow injection analysis (FIA) system was employed to achieve automated, rapid, and reproducible Pb²⁺ detection. The proposed sensor exhibited a low detection limit of 0.08 nM and two distinct semi-logarithmic linear dynamic ranges, namely a low-concentration range (1.0-100 nM) and a high-concentration range (1.0-100 μM), each confirmed by its respective calibration plot. The sensor demonstrated satisfactory reproducibility and stability. Interference studies confirmed high selectivity toward Pb²⁺ in the presence of ten potentially interfering metal ions (Co²⁺, La³⁺, Ni²⁺, Li⁺, Zn²⁺, Cu²⁺, Er³⁺, Ca²⁺, Mn²⁺, and Sn²⁺), each evaluated at up to 50-fold excess concentrations. Application to real water samples resulted in recovery values ranging from 93% to 107%, demonstrating the accuracy and practical applicability of the proposed method for environmental monitoring.