Due to specific metal ion complexation abilities of macrocyclic crown ethers, extensive studies of ion-selective electrodes based on these interesting ion carriers have been carried out [1]. These type of ligands are capable of selective and efficient transport of alkali and alkaline earth cations across membranes and, thus, have been widely used in the construction of PVC-based membrane electrodes for these cations[2]. However, the complexation ability of crown ethers toward soft heavy metal ion is quite low. This problem has been overcome by substitution of some oxygen atoms of crown ethers by sulphur atoms which results in a considerable decrease in the stability of cations such as alkali and alkaline earth ions [3], but unfortunately increase in the stability of cations such as Tl+ and Hg2+ ions in solution[4]. In recent year we used dibenzyldiaza-18-crown-6 (DBzDA18C6) as an excellent carrier in construction of a novel silver-PVC membrane electrode. The sensor exhibits a very good response for Ag+ in a wide concentration range from 3.16 × 10-6 – 1.9×10-2 M with a slope of 57.6 ± 0.5 mV / decade of Ag+ concentration. The response time of sensor is < 10 s, and the membrane can be used for more than 3 months without any observed divergence in potentials. The proposed sensor exhibits very good selectivity for Ag+ over other cations and can be used in a wide pH range (3.0-7.5). It has also been possible to use this assembly as an indicator electrode in potentiometric titrations involving silver ions References 1. K. T. Chono, in Binding by Macrocycles (Eds.: Y. Inoue, G. W. Gokel), Marcel Dekker, New York, 1990. 2. E. Bakker, P. Buhlman, E. Pretsch., Chem. Rev, 7, 3083 (1997) 3. R.M. Izatt, J.S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen, D.Sen, Chem. Rev, 85, 271 (1985) 4. R. M. Izat, K. Pawlak, J.S. Bradshaw, J. S. Bruening., Chem. Rev, 91, 1721 (1991) 5. M.H. Mashhadhzadeh, M. Shamsipur., Anal. Chim. Acta, 381, 111 (1991)
