The need of selective determination of heavy metal ions has increased immensely during the last few decades due to the growing environmental problems [1]. Among heavy metals, the pollution caused by cobalt is of considerable concern. Determination of cobalt assumes importance because of its widespread occurrence in sea as well as in fresh water, earth crust, meteorites, animals and plants [2]. Potentiometric sensors based on ion-selective electrodes are especially suited for such determination because they offer advantages such as selectivity, sensitivity, good precision, simplicity and low cost [3, 4]. In this study, a graphite membrane based on 1,13-bis(8-quinolyl)-1,4,7,10,13-entaoxatridecane (Kryptofix 5) with NaTPB, graphite powder (GP) , oleic acid (OA), palmitic acid (PA) as additive and dibutylphthalate (DBP), dioctylphthalate (DOP), bis(2-ethylhexyl) sebacate (DOS), Dibutyl sebacate (DBS), onitrophenyloctyl ether (o-NPOE), acetophenone (AP) and nitrobenzene (NB) as plasticizing solvent mediators were prepared and investigated as Co2+ selective electrode. Then, the graphite rod was coated by coating of the membrane with Dip/Dry method. Under the optimized conditions, the electrode 81 exhibits a nernstian slope(30±0.3 Mv/decade) with fast response time of about 30s. The effect of the various parameters, e.g. effect of pH, effect of time and etc, have been established and optimized. Potentiometric selectivity of the CGE for cobalt over other interfering ions are determined. This electrode reveals a very good selective toward cobalt(II) ion over a wide range of alkali, transition and heavy metal cations. Application of this electrode for the determination of cobalt in real samples and as indicator electrode for potentiometric titration of cobalt solution with EDTA are reported.

Keywords