Abstract
For the study of a hydrodynamic electrode, an apparatus with a working electrode of a running gold wire loop was constructed, and the basic characteristics of this system were discussed in the case of the automatic stripping analysis of lead ion.
In this apparatus, the running wire electrode passes through the cleaning electrolytic cell, the electrode-position cell, and the electrodissolution cell in turn. Each of the deposition and the dissolution cells is divided by a sheet of cation-exchange membrane into the room of the running wire electrode and the room of an Ag-AgI counter electrode, which serves as the reference electrode. The standard electrolyte solution {1 × 10-3 or 1 × 10-4 M Pb(NO3)2, 0.1 M KNO3, pH 4 with HNO3} is fed to the deposition cell and an electrolyte solution (0.1 M KNO3, pH 4 with HNO3) is also fed to the dissolution cell from a constant head, but the electrolyte solutions in the rooms of the counter electrodes (1 M KI) are circulated with the respective tube pump.
The cleaning electrolytic cell is separated into three chambers along the wire electrode, and each of the chambers contains a platinum counter electrode. The counter electrode in the central chamber is connected to the positive terminal of a constant current source, and the other two are connected to the negative terminal. The gold wire working electrode is thus cleaned electrolytically on passing through the three chambers.
The main feature of this apparatus is that the solid electrode with pretreated surface is automatically passed through the deposition and the dissolution cells filled with electrolyte solutions. In this system the renewal of the surface of the working electrode causes no increase in the charging current because the capacitance of the electric double layer does not change. Since the most promising analytical application of this system is that to the stripping method, an automatic stripping analysis of lead ion was studied in detail.
Although the deposition current due to the reduction of lead ion flowing through the deposition cell was not observed clearly because hydrogen was evolved by the cathodic polarization of the running electrode, the anodic dissolution current through the dissolution cell was determined clearly enough. The recoveries of the electrode position were 1.9% for 1 × 10-3 M and 5.4% for 1 × 10-4 M lead ion when the flow rate of the sample solution was 27 ml/min and the running speed of the wire electrode was 20 mm/min. On the other hand, the ratio of the dissolution current to the deposition current remained fairly constant.
In order to increase the repoducibility it is necessary to make the stream of the electrolyte solutions uniform in the deposition and dissolution cells and to increase the running speed of the electrode.
