Recently, several greatly selective and sensitive poly(vinyl chloride) (PVC)-membrane ISEs for various metal ions have been reported[1,2]. In this study, the coated graphite electrode(CGE) for determination of mercury(II) was prepared based on 1,13-bis(8-quinolyl) -1,4,7,10,13-pentaoxatridecane(kryptofix5) as an excellent sensing material is successfully developed. It is well established that some important features of the PVC membranes such as the properties of the plasticizer, the plasticizer/PVC ratio, the nature and amount of the ion carrier, and particularly the nature and amount of the additives used, significantly influence the sensitivity and selectivity of the ion-selective electrodes[3]. The construction, performance characteristics, and application of a novel mercury(II) membrane sensor are reported in this paper. Different aspects for the preparation of Hg(II) sensors based on kryptofix5 were optimized. Effects of various plasticizers was studied in detail and improved performance was observed. In our preliminary studies, to examine the interactions between Hg2+ cations and the ligand, complex formation between the ligand and mercury(II) cations was investigated. The best performance was obtained for the membrane sensor having a composition of 30% poly(vinyl chloride) (PVC), 65% dibutyl phetalat(DB), 5% 1,13-bis (8-quinolyl)-1,4,7,10,13- pentaoxatridecane(kryptofix5) and 2% sodium tetraphenyl borate (NaTBP). The electrodes exhibit Nernstian slope of 30.8 ± 0.3 mV per decade for Hg2+ ions over wide concentration range(1.0×10−2 to 1.0×10−7M). The CGE have detection limits of 5.0×10−7M, and response times of about 15s and can be used for at least2 monthes without noticing any considerable potential divergence. The potentiometric response is independent of the pH of the test solution in the pH range 3.0–8.0. The potentiometric selectivity coefficient values as determined by match potential method(MPM) indicate excellent selectivity for Hg2+ ions over interfering cations. In addition, The proposed electrode revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The CGE was used as indicator electrode in the potentiometric titration of Hg2+ ions with EDTA. The sensor possessed the advantages of short conditioning time, fast response time and, especially, good selectivity towards the transition and heavy metal ions as well as some mono, di and trivalent cations such as Na+, K+, Pb2+, Ni2+, Co2+, Zn2+, Cu2+, Mg2+, Fe3+, Al3+and Cr3+. The sensor accuracy was investigated by the potentiometric titration of a Hg2+solution with sodium sulfide and sodium chlorid as well as the monitoring of Hg(II) cations. As a result, the developed sensor provided satisfactory results after its application in the Hg2+ determination in waste water samples.

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