Comparative Studies of Neodymium (III) Selective Poly(vinyl chloride) Electrodes Based on O, N, S Donor Ionophores

Abstract

Two Schiff-base chelates 4-Methoxy-2-{((2-(pyridin-2-yl)ethyl)sulfanyl}ethyl) iminomethyl phenol (L1), and 2,2'-{sulfanediylbis (ethane-2,1-diyinitro methylylidene)}-diphenol (L2) have been synthesized and used as neutral carrier for the fabrication of Nd(III) selective membrane electrode. The values of formation constant indicates that the proposed ionophore forms stable complex with Nd(III). The addition of sodiumtetraphenylborate and various plasticizers, viz., o-NPOE TBP DBBP TEP and DOS has been found to substantially improve the performance of the electrode. The best performance was obtained with the electrode no.6 having membrane of ionophore (L2) with composition PVC: o-NPOE: ionophore (L2): NaTPB (%, w/w) of 32: 61:5:2. This electrode exhibits Nernstian response with slope 21.1 ± 0.3 mV decade -1 of activity in concentration range 1.6 x 10 -8 to 1.0 x 10 -1 M Nd(III), performs satisfactorily over wide pH range ( 2.5 - 8.3.), with a fast response time (8s). The elec- trode was also found to work satisfactorily in partially non-aqueous media up to 20% content of methanol, ethanol or acetone and could be used for a period of 5 weeks without any change in response characteristics. The Nd(III) selective electrode was used as an indicator electrode for the titration of 50 ml 1 x 10 -3 M EDTA solution. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The application of prepared electrode has been demon- strated in the determination of neodymium (III) in monazite, bastnasite and spiked water sample.