Iodide Selective Electrodes Based on Bis(2-mercaptobenzothiazolato) Mercury(II) and Bis(4-chlorothiophenolato) Mercury(II) Carriers

Abstract: New iodide-selective electrodes based on bis(2-mercaptobenzothiazolato) mercury(II) [Hg(MBT)₂] and bis(4-chlorothiophenolato) mercury(II) [Hg(CTP)₂] carriers are described. The electrodes were prepared by incorporating the ionophores into plasticized PVC membranes, which were directly coated on the surface of graphite disk electrodes. The electrodes displayed high selectivity for iodide with respect to a number of inorganic and organic anions. The influence of the membrane composition and pH, and the effect of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The electrodes exhibited near-Nernstian slopes of -57.6 ± 0.8 and -58.4 ± 1.4 mV/decade of iodide concentration over the range 1 × 10^-6 – 1 × 10^-1 M, with detection limits of ~4 × 10^-7 and 6 × 10^-7 M for the electrodes based on [Hg(MBT)₂] and [Hg(CTP)₂], respectively. They have relatively fast response times (≤ 10 s), satisfactory reproducibility, and life times of at least two months. The potentiometric responses of the electrodes are independent of pH of the test solution over the range 3.5 – 11.5.