Macrocyclic compounds, due to their selective receptor properties and ease of structural modification, have been employed as ionophores in construction of ion selective electrodes for the determination of alkali, alkaline and many transition metal ions [1-3]. A cerium(III) cation selective electrode based on 1,13- bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) incorporated into a poly(vinyl chloride) (PVC) membrane has been developed. The electrode was prepared by coating the surface of a graphite rod by a membrane containing dioctylphtalate(DBP) as plasticizer, 1,13-bis(8-quinolyl)-1,4,7,10,13- pentaoxatridecane (kryptofix5) as an ionophore, sodium tetraphenyl borat(NaTPB) and poly(vinyl chloride) (PVC) in tetrahydrofuran (THF). The best composition of the coated membrane (w/w%) was found to be: 3% ionophore, 65% plasticizer, 30% PVC and 2% sodium tetra phenyl borat. In the present work, we investigated on Ce3+ coated graphite electrode and the proposed electrode could form the base of easily made electrodes, because it is used in the form of solid state coated-conductor. Ion selective electrode prepared by coating polymeric membrane films containing electroactive species directly on the surface of a conducting substance such as graphite. In our preliminary studies, to examine the interactions between Ce(III) cations and the ligand, the complex formation between the ligand and cerium(III) cation was investigated. For this purpose, a conductometric titration was performed, and the change in molar conductivity (Λm) versus the ligand to cation molar ratio([L]t/[M]t) was studied to determine the stability constant of the complexation of 1,13-bis(8-quinolyl)- 1,4,7,10,13-pentaoxatridecane (kryptofix5) with cerium(III) cations in acetonitrile (AN). The stoichiometry of the complex formed between cerium(III) cation and kryptofix5 was 1:1. The constructed electrode exhibits a Nernstian slope (19.9±2 mv) over the concentration range from 1.0×10−2 to 1.0×10−5 M. The detection limit of the electrode is 1.0×10−5 M. The effects of the pH and the possible interfering cations and anions were investigated and the optimized conditions for electrode were evaluated. It was concluded that the sensor response was pH independent in the range of 2.5–7. The response time of the 138 electrode is about 15 s and it can be used for more than 6 weeks without observing any divergence in potentiometric response. The sensor accuracy was investigated in the potentiometric titration of a Ce (III) solution with EDTA. Additionally, the proposed sensor was used in the potentiometric titration of potassium boromide, potasium iodide and sodium chloride.

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