Application of thallium(I) as an internal standard redox process in voltammetric measurements

The quality of voltammetric measurements can be improved by the application of thallium(I) as an internal normalization indicator standard redox process. Current fluctuations caused by unstable experimental parameters, such as the drop size of the hanging mercury drop electrode and the hydrodynamics of the system, are depressed when the ratio of the signals of the investigated and the indicator electrode processes is used for the analysis. This advantage can be attributed to the partial correlation of these two signals fluctuations. Results of repetitive measurements of copper(II) and lead(II), the standard addition method used for analytical determination of concentration of copper(II) in a sample, and pseudopolarographic measurements of copper(II), with the addition of thallium(I) as the internal standard redox process are presented. A test procedure, to decide whether the indicator process itself has undergone some systematic changes and is qualified for data normalization, is proposed. The limits of the proposed procedure are encountered when the two signals are too close and when the variations of the repeated measurements for the two signals are not correlated.