A new solid contact cobalt selective electrode was constructed with 4-tert-butylthiacalix[4]arene as ionophore. The best performance was observed with the membrane having an ionophore/polyvinyl chloride/sodium etraphenylborate/nitrophenyl octyl ether ratio of 3.5:33:1.5:62 (w/w; mg). The electrode, under steady-state conditions, exhibited a working concentration range of 1 101 e 1 106 mol…