Voltammetric determination of the iodide ion with a quinine copper(II) complex modified carbon paste electrode

A Cu(Qui)(NO₃)₂ modified-carbon paste electrode (where Qui is quinine) was constructed by incorporating Cu(Qui)(NO₃)₂ into a carbon-paste composed of graphite powder and Nujol. The modification with Cu(Qui)(NO₃)₂ resulted in a deposit of iodide ions on the electrode surface through a ligand exchange reaction. This exchange reaction was completed within 20 ms in a CHCl₃+CH₃OH solution. The rate constant, k⁰, of the ion exchange reaction was determined to be 27 s^?1 by the stopped flow spectroscopic method. The anodic peak of the pre-deposited iodide ion on the electrode surface was observed at +0.54 V in a cyclic voltammogram. Various experimental parameters such as pH, deposition time, temperature, and electrode composition were optimized to analyze the iodide ion employing linear sweep and differential pulse voltammetry. With the exception of thiosulfate ions, inorganic anions did not interfere with the determination of the iodide ion. Using linear sweep voltammetry, a calibration curve was attained over the concentration ranges of the iodide ion from 1.0×10^?4–2.5×10^?6 M at the deposition time of 10 min, with the detection limit determined as 1.0×10^?6 M. Using differential pulse voltammetry, the logarithmic linear response range for the iodide ion was between 10^?6 and 10^?8 M, and the detection limit was 1.0×10^?8 M. This method was evaluated by analyzing the iodide ion content in a commercial disinfectant.