The use of EQCM for setting the optimum conditions of the determination of Pd2+ ions via its palladium–histidine complex

Electrochemical quartz crystal microbalance (EQCM) was used as a novel approach for the determination of palladium–histidine complex formation on an amalgam film gold based electrode. We have demon- strated the applicability of an amalgam-modified gold QCM substrate to monitor histidine adsorption and palladium ions complexation under electrochemical control. The results of EQCM measurements re- vealed that adsorption of histidine on amalgam film gold based electrode is dependent on the potential, indicating that the electrosorption occurs which depends on the charge on the gold–mercury surface and the charge of the histidine ions. The interactions of palladium ions with the adsorbed layer of histidine at open circuit potential results in the removal of histidine from mercury surface, indicating stronger bonds between histidine and palladium than between histidine and mercury. On the other hand, by applying the potential of −200 mV upon the introduction of palladium ions it is possible to obtain histidine-palladium complex adsorbed on the mercury surface. This phenomenon was used for the determination of Pd using adsorptive stripping voltammetry (AdSV). Application of the deposition potential indicated by EQCM led to well defined analytical signals increasing with standard addition.