Novel solid-state cadmium ion-selective electrodes based on its tetraiodo- and tetrabromo-ion pairs with cetylpyridinium

Two novel cadmium solid-state ion-selective electrodes have been prepared by coating the surface of a graphite rod electrode directly with tetrahydrofuran solution containing PVC, cetylpyridinium–tetraiodocadmate (I) or cetylpyridinium–tetrabromocadmate (II), dioctyl phthalate and sodium tetraphenyl borate. The two sensors exhibit near-Nernstian anionic slopes of −29.8 and −25.1 mV/concentration decade, independently of pH over a wide range, with very fast response times of 3 and 7 s, respectively. The tetraiodocadmate (TIC) and tetrabromocadmate (TBC) electrodes posses linear ranges of 1.5 × 10−6–1 × 10−1 and 1.0 × 10−6–1 × 10−1 M and lower detection limits (LDL) of 6 × 10−7 and 8 × 10−7 M, respectively. The effects of membrane composition, type of plasticizer and pH of the sample solution were investigated thoroughly. The TBC electrode is shown to be free of all interference that is common for most of the reported cadmium ISEs except for that of Hg2+ ion. The two electrodes were applied for the determination of cadmium in some alloys and polluted water.