Novel lanthanum(III) membrane sensor based on a new N-S Schiff’s base

A novel lanthanum(III) sensor based on bis(thiophenal)phenylen-1,3-diamine (TPD) is described. The sensor was prepared by incorporating the TPD into plasticized PVC membrane. The sensor displays high selectivity for lanthanum with respect to many common alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of were investigated. The sensor with 35% PVC, 54% solvent mediator, 8% ionophore and 3% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.6 mV per decade) over the concentration range 1.0×10−7 to 1.0×10−1 M. The detection limit of the electrode is 2.0×10−8 M (∼3.0 ng/ml). The response time of the electrode is very fast (10 s) in whole concentration range. The sensor can be used in the pH range 3.5–9.5 for at least 2 months. The membrane sensor was used as an indicator electrode in potentiometric titration of lanthanum ions with EDTA. It was successfully applied in determination of fluoride ions in mouth wash preparations.