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A new polyvinyl chloride (PVC) membrane electrode that is highly selective to Fe(II) ions was prepared using N-phenylaza-15-crown-5 (NPA15C5) as a suitable neutral carrier. The sensor exhibits a Nernstian response for Fe(II) ions over a wide concentration range (1.0 Â 10À2 to 1.0 Â 10À6 M) with a slope of 29.2 ± 0.6 mV per decade. It has a response time of <15 s and can be used for at least 2 months without any measurable divergence in potential. The proposed sensor shows a fairly good discriminating ability towards Fe2+ ion in comparison with some hard and soft metal ions. The isothermal temperature coefficient of this electrode amounted to 0.0017 V/8C. The stability constant (log Ks) of the Fe(II)–NPA15C5 complex was determined at 258C by potentiometric titration in mixed aqueous solution. The results show that this electrode can be used in ethanol and dioxane media up to 20% and 5% (v/v) concentration, respectively, without interference. The electrode was used for direct determination of Fe2+ in the ferrous sulfate syrup.

The main advantages of the proposed potentiometric sensor are its simplicity of preparation, short conditioning time, fast response time, wide dynamic range, low detection limit, low cost, Nernstian behavior, and fairly good selectivity. The electrode performs successfully in partially non-aqueous medium. The electrode has a life- time of more than two months. The electrode also was successfully applied to the direct determination of Fe(II) in the ferrous sulfate syrup. Acknowledgment The authors are highly thankful to Islamic Azad University of Lahijan for supporting assistance to complete this work.