Electroanalytical studies on cobalt(II) selective potentiometric sensor based on bridge modified calixarene in poly(vinyl chloride)

A bridge modified 4-tert-butylthiacalix[4]arene (I) has been employed as electroactive material in the preparation of cobalt selective sensor. Polyvinyl chloride (PVC)-based membranes of (I) using sodium tetraphenylborate (NaTPB) as anion discriminator and bis(2-ethylhexyl) sebacate (DOS), chloronaphthalene (CN), tri-n-butylphosphate (TBP), o-nitrophenyl octyl ether (NPOE), tris(2-ethylhexyl)phosphate (TEHP) as plasticizers were prepared and investigated as cobalt selective sensors. A number of membranes of different compositions were prepared and investigated. The best performance was observed with the membrane having composition of 2:66:1.5:127 (mg) = I:NaTPB:PVC:NPOE. The potential response of this membrane is linear to Co2+ ions in the concentration range 5.3 × 10−6 to 1.0 × 10−1 M with near-Nernstian slope of 30.0 mV/decade of activity and a detection limit of ∼0.3 ppm. This membrane also showed lowest response time of 10 s and works satisfactorily in partially non-aqueous medium. The selectivity studies of this sensor, evaluated with fixed interference method and matched potential method, show that the sensor under consideration possesses excellent selectivity for Co2+ over a large number of mono-, bi- and trivalent cations such as Na+, K+, Ag+, Ca2+, Mg2+, Cu2+, Hg2+, Pb2+, Li+, Ba2+, Zn2+, Sr2+, Cr3+, Ni2+, etc. The sensor could be used as an indicator electrode in the quantification of Co2+ by potentiometric titration against EDTA as well as in determination of cobalt content in wastewater and beer samples.