Sub-Micro Molar Monitoring of La³⁺ by a Novel Lanthanum PVC-Based Membrane Sensor Based on 3-Hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide

A La (III) ion-selective membrane sensor has been fabricated from poly vinyl chloride (PVC) matrix membrane, containing 3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide (HPMN) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as an anionic excluder and orthonitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of membrane composition and pH as well as the influence of the anionic additive on the response properties were investigated. The sensor with 30% PVC, 62% solvent mediator, 6% ionophore and 2% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.2 mV per decade) across the range of 1.0 x 10^-2 - 1.0 x 10^-7 M. The detection limit of the electrode is 7.0 x 10^-8 M (∼10 ng/mL) and the response time is 15 s from 1.0 x 10^-2 up to 1.0 x 10^-4 M and 30 s in the range of 1.0 x 10^-5-1.0 x 10^-7 M. The sensor can be used in the pH values of 3.0-9.0 for about seven weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of lanthanum ions with EDTA. It was successfully applied to the lanthanum determination in some mouth wash preparations