A Liquid membrane based electrode containing an electroactive chelating substance selective for cobalt (II) ions Full Paper INTRODUCTION Cobalt is essential in trace amounts for human life. Cobalt is essential for the growth of red blood cells in the body hence used as the treatment for anemia. The toxicity of cobalt is quite low compared to many other metals in soil. Exposure to very high levels of cobalt can cause health effects like effects on lungs, including asthma, pneumonia and wheezing. Cobalt is widely dis- tributed in the environment and the average abundance of cobalt in earth crust is 29ppm, 1.0 to 14ppm in soil, 0.2ppm streams, 1 to10ppm in ground water [1] . It is Nidhi Rani Gupta 1 , Susheel K.Mittal 1 *, Subodh Kumar 2 , S.K.Ashok Kumar 1 1 School of Chemistry and Biochemistry, Thapar University, Patiala, 1470 01, Punjab, (INDIA) 2 Department of Chemistry, Guru Nanak Dev University, Amritsar-143005, (INDIA) Fax: +91-175-2364498 E-mail: smittal@tiet.ac.in Received: 26 th October, 2007 ; Accepted: 31 st October, 2007 widely used in various alloys like, steels, in electroplat- ing, in fertilizers, and in porcelain glass [2] . Most of co- balt consumed is used in the manufacture of alloys, and although not released extensively in the environment, it may represent a hazard to human health. Higher expo- sures can occur for workers who are exposed to co- balt in industries that process it or make products con- taining cobalt. Cobalt is considered essential for algae, some bac- teria and for animals. Occupational toxicology of co- balt, hygienic and epidemiologic aspects, and monitor- ing of cobalt poisoning are also topics of special inter- KEYWORDS Poly vinyl chloride (PVC); Ionophore; Liquid membrane; Selectivity coefficients; Indicator electrode; Cobalt ions. ABSTRACT Spectrophotometric and conductometric studies on the binding proper- ties of 1,4,8,11-tetraazacyclotetradecane-5,7-dione (I) toward Co 2+ and dif- ferent metal ions have been done. Data revealed the occurrence of 1:1 (ligand/metal ion) complexation with a stability order of Co 2+ >Cu 2+ >Pb 2+ > Ni 2+ >Ag + . Consequently, (I) was also used as a neutral carrier for the preparation of a novel liquid membrane based electrode selective for Co 2+ ions. The electrode revealed a Nernstian slope 31mV/decade over wide concentration range 1.010 -6 - 1.010 -1 M and detection limit 5.010 -7 M. It has response time of <10 sec and can be used over a constant pH range of 5.0-8.0. The electrode possesses a fast response time and can be used for at least 4 months without observing any considerable deviation in the response behavior and selectivity. Electrode shows a very good selectiv- ity for Co 2+ over a number of alkali, alkaline earth, transition, and heavy metal ions. The proposed electrode was successfully applied as an indica- tor electrode, in potentiometric titration of Co 2+ ions with ethylene diamine tetra acetic acid (EDTA).  2008 Trade Science Inc. - INDIA Trade Science Inc. ACAIJ, 7(4) 2008 [179-184] An Indian Journal Volume 7 Issue 4 January 2008 Analytical CHEMISTRY Analytical CHEMISTRY