Potentiometric method based on ion selective electrodes compare with other methods of analysis have several advantages including : simplicity, speed and low cost[1]. In this work we have designed and constructed a coated membrane electrode for measuring the yttrium(III) ion activity by using dibenzo-18- crown-6 in aqueous solutions.Dibenzo-18-crown-6 (DB18C6) 3% has been used as membrane carrier (ionophore), nitrobenzene (NB) as plasticizer 65%, sodium tetraphenyl borate(NaTPB) as lipophilic anion 2% , poly vinyl chloride (PVC) 30% as matrix and tetrahydrofuran (THF) as a solvent[2]. The graphite rod was then coated by coating of the membrane with Dip/Dry method[3].The results of calibration curve for this electrode at the optimized conditions exhibit a Nernstian response of 17.5±0.5 mV for Y3+ ion over a wide linear dynamic range from 1×10-2-1×10-5 M at 25°C.It was concluded that the sensor potentiometric response is independent on the pH of the solution in a wide range of 6-11 .The detection limit for this electrode is 1×10-7.Furthermore,the proposed sensor presented a relatively fast response time of 30s.Concerning the electrode lifetime, no considerable potential divergence was noticed for at least 50 days. The effect of the interfering ions and the selectivity of electrode were also studied. Noticeably, the electrode revealed comparatively a good selectivity for Y(III) ions with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. This sensor was effectively used as an indicator electrode in the potentiometric titration of Y(III) ions with EDTA, NaCl, Li2CO3.The constructed sensor accuracy was investigated by the monitoring of Y(III) ions in mixtures of three and five different ions.

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