Parasitic resistance as a source of error in voltammetric measurements

Differential pulse and square wave polarographic/voltammetric measurements were performed in the Pb2+-Cl− system in order to find the origin of the inconsistency observed in previous results concerning the adsorption of lead(II) on mercury electrodes. For such a purpose different static mercury drop electrodes (SMDEs) and two different polarographic analyzers were used. The final conclusion is that no adsorption effects can be observed under the chosen conditions and the opposite results should be treated as artefacts, connected with the iR drop inside the applied electrode system. The disturbances were eliminated by cleaning the inner parts of the SMDE, and restored after the insertion of well defined resistors in the measuring circuit. Some model calculations with included iR drop losses have given the same distortion of current-voltage characteristics. As a result, a procedure for testing the correctness of the electrode system before starting each new series of measurements, is proposed.