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 x 10(-2) to 1.0 x 10(-6) 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/degrees C. The stability constant (log K-s) of the Fe(II)-NPA15C5 complex was determined at 25 degrees C 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.