A novel gadolinium ion-selective electrode based on the antibiotic omeprazole as membrane carrier was prepared. The electrode has a linear dynamic range between 1.0 Â 10 À1 and 1.0 Â 10 À5 M, with a Nernstian slope of 19.3 AE 0.3 mV decade À1 and a detection limit of 5.0 Â 10 À6 M. The potentiometric response is independent of the pH of the solution in the pH range 4.0 ± 10.0. The electrode possesses the advantages of short conditioning time, fast response time and especially, very good selectivity over a large number of other cations. The electrode can be used for at least 2 months without any considerable divergence in potentials. It was used as an indicator electrode in potentiometric titration of Gd(III) ions with EDTA.

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