Rubeanic acid as novel carrier in construction of selective membrane sensor for La(III)

A new polyvinylchloride-based membrane of rubeanic acid as an ion carrier was fabricated using oleic acid as lipophilic additive. The best performance was exhibited by the membrane having composition rubeanic acid:PVC:OA:o-NPOE as 5:180:18:208 (w/w). The sensor exhibited a Nernstian response for La3+ over a wide concentration range of 3.2 × 10−8 to 1.0 × 10−2 M with a detection limit of 2.5 × 10−8 M. It showed response time of less than 15 s and could be used for 5 months without any significant divergence. The proposed membrane sensor revealed good selectivity for La3+ over a wide variety of other metal ions and can be used in a pH range of 3.5-9.5 and in mixtures containing up to 30% (v/v) non-aqueous content. It was successfully used as an indicator electrode in the potentiometric titration of La(III) against EDTA.