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-butyl phosphate (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 x 10(-6) to 1.0 x 10(-1) M with near-Nernstian slope of 30.0 mV/decade of activity and a detection limit of similar to 0.3 ppm. This rnembrame also showed lowest response time of 10s 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. (c) 2008 Elsevier Ltd. All rights reserved.