Preconcentration and voltammetric behaviour of Ag+ at carbon paste electrodes modified by N-benzoyl-N′,N′-di-i-butyl-thiourea

The preconcentration of silver at carbon paste electrodes (CPE) modified with N-benzoyl-N′,N′-di-i-butyl-thiourea and its subsequent voltammetric determination is studied with test solutions. The preconcentration of silver at the surface of the modified CPE succeeds as well with open circuits as with applied potentials. The amount preconcentrated depends on the electrode potential with a maximum at +0.1 V vs. Ag/AgCl, thus enabling the preconcentration of silver without cathodic treatment. The detection limit is in the order of 10–4 mmol/l Ag+. The surface reactions during the preconcentration are discussed. It is assumed that silver complexes of the modifier are formed in a fast reaction followed by a slow reaction with participation of silver and of carbon surface groups.