Ion-Selective Electrode for Lanthanum Determination in Standard Samples

Abstract

A poly(vinyl chloride)-based membrane of 5,14-N,N′-hydroxyphenyl-4,15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTH) with sodium tetraphenyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dibutyl butylphosphonate (DBBP), tris(2-ethylhexyl) phosphate (TEP) and tributyl phosphate (TBP) as plasticizing solvent mediators was prepared and investigated as a La(III)-selective electrode. The best performance was observed with the membrane having the ligand-PVC-DBP-STB composition 2:10:7:1, which worked well over a wide concentration range (1.77 × l0−6– 0.1 mol L−1) with a Nernstian slope of 20 mV per decade of activity between pH 3.0 and 6.5. This electrode showed a fast response time of 15 s and was used over a period of 4 months with good reproducibility (s = 0.4 mV). The selectivity coefficients for mono-, di- and trivalent cations indicate excellent selectivity for La(III) ions over a large number of cations. The sensor has been used as an indicator electrode in the potentiometric titration of La(III) with EDTA. The practical utility of the membrane sensor has also been observed in the determination of lanthanum in monazite sand and standard samples.