Iron(III) ionophores based on formylsalicylic acid derivatives as sensors for ion-selective electrodes

Novel iron(III)-selective PVC membrane electrodes based on formylsalicylic acid derivatives were studied. The electrode based on p-chloroaniline-3-formylsalicylic acid as a sensor, containing potassium tetrakis(4-chlorophenyl)borate as a lipophilic salt and o-nitrophenyl octyl ether as a plasticizer, gave the best performance. The electrode exhibits a good Nernstian response for 10(-1)-5.0 x 10(-5) mol l(-1) FeCl3 with a slope of 20 mV per decade. It shows a high selectivity for iron(III) in comparison with alkali, alkaline earth and heavy metal ions. The electrode response and selectivity remained almost unchanged for at least 1 month. The effects of plasticizers, membrane supports, lipophilic salts and pH on the potential response of the electrode were also studied. The electrode was successfully applied to the determination of iron(III) contents in some rocks.