Lead-selective poly(vinyl choride) membrane electrodes based on heterocyclic thiocarboxylic acid

Abstract

Heterocyclic thiocarboxylic acids have been designed to prepare polymeric membrane ion-selective electrode (ISE) for Pb2+. Construction, response characteristic and application of the lead ISEs are investigated. Better results have been obtained with membranes containing ligands L1∼L3 with bis(2-ethylhexyl) sebacate (DOS) as a plasticizer. Ionophores L1∼L3 are [(4,6-dimethyl-2-pyrimidinyl) thio] acetic acid (L1), (1,3,4-thiadiazole-2,5-diyldithio) diacetic acid (L2) and (1,3,4-thiadiazole-2,5-diyldithio) dipropionic acid (L3). The optimum electrodes have the composition of L1 (1.6): PVC (32.7): DOS (65.3): KTp ClPB (0.4) (w/w), L2 (1.0): PVC (32.8): DOS (66.0): KTpClPB (0.2) (w/w), and L3 (1.0): PVC (32.7): DOS (65.4): KTpClPB (0.9) (w/w). The optimized membrane electrodes work well over a wide range of concentrations (1.0 × 10−5 ∼1.0 × 10−2 M, 1.0 × 10−6 ∼1.0 × 10−2 M, and 1.0 × 10−6 ∼1.0 × 10−2 M) with the response slope of 27.4, 30.1 and 29.2 mV/decade, respectively. Potentiometric selectivities of the ISEs based on L1 ∼ L3 for Pb2+ over other interfering ions are determined with the fix interference method. The electrodes display good selectivity over a number of alkali, alkaline earth, transition and heavy metal ions. The lifetime of the electrodes is about 2 months and their response time is 20 s. Applications of these electrodes for the determination of lead in real samples and as indicator electrodes for potentiometric titration of Na2SO4 using Pb2+ solution are reported.