Lanthanum(III) Ion Selective Electrode Based on a New Ionophore

A PVC membrane electrode based on ۱-[({[(butylsulfunyl)carbothioyl]disulfanyl} carbothioyl)sulfanyl]butane as a suitable ion carrier for determination of lanthanum(III) ion was prepared. This electrode revealedsuch a good selectivity toward La۳+ ion over a wide variety of other metal ions. Some experimental parametersuch as membrane composition, nature, and amount of plasticizer, the amount of additive, and concentrationof internal solution on the potential response of La۳+ sensor were investigated. The electrode exhibits aNernstian slope of ۲۰.۹±۱.۸ mV per decade of La۳+ over a wide concentration range ۳.۳×۱۰-۷-۱.۰×۱۰-۲ M inthe pH range ۳.۷-۷.۳. The response time is about ۷s and detection limit is ۲.۵ ×۱۰-۷ M and it can be used forat least ۱month without any considerable divergence in potential. It was used as an indicator electrode inpotentiometric titration of lanthanum(III) ion with EDTA.