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

A PVC membrane electrode based on 1-[({[(butylsulfunyl)carbothioyl]disulfanyl} carbothioyl)sulfanyl] butane as a suitable ion carrier for determination of lanthanum(III) ion was prepared. This electrode revealed such a good selectivity toward La3+ ion over a wide variety of other metal ions. Some experimental parameter such as membrane composition, nature, and amount of plasticizer, the amount of additive, and concentration of internal solution on the potential response of La3+ sensor were investigated. The electrode exhibits a Nernstian slope of 20.9±1.8 mV per decade of La3+ over a wide concentration range 3.3×10-7-1.0×10-2 M in the pH range 3.7-7.3. The response time is about 7s and detection limit is 2.5 ×10-7 M and it can be used for at least 1month without any considerable divergence in potential. It was used as an indicator electrode in potentiometric titration of lanthanum(III) ion with EDTA.