Platinum wire electrodes coated with mercury

The development of the reductive mode LCEC technique has been slow because of difficulties in preparing convenient and reliable working electrodes for use with a high efficiency chromatographic separation. In addition, problems are encountered with dissolved oxygen and heavy metals. Solid electrodes have been used with limited success for reductive LCEC. Mercury pool electrodes (44-47), the DME (48-53), and platinum wire electrodes coated with mercury (49) are generally not satis-... 

Sample cells (Figure 5.16) were constructed upon the coated panels by glueing the polished end of glass tubes (internal diameter about 50 mm.) onto the coated surface with epoxy cement. The sample cells were stored at 22 2°C and a relative humidity of 55 + 5 per cent. The steel panel served as high potential electrode (H), and a mercury electrode, connected by a platinum wire, as low potential electrode (L). Guarding was achieved by using a bell-shaped brass cover which also supports the connector of the low potential electrode. 

Anodic stripping voltammetry was in use already in 1972 to determine Bi in plasma [120]. Bismuth is one of the elements most easily determined with this method. It can be deposited on electrodes at potentials at which most other elements ate in solution. Glassy carbon electrodes coated with films of mercury [100,121-124], but also of gold [101,125], are used. As reference served calomel or silver/silver chloride electrodes [121]. Platinum foils or wires were used as counterelectrodes. At -0.7 V carbon electrodes are precoated with mercury from acid Hg(II) or gold from acid Au(III) solutions. To deposit Bi on the electrode -0.2 to -0.3 V is a sufficient potential for preelectrolysis, but mostly higher voltages are chosen to determine other metals as well. Bi is stripped fiom the electrode at potentials of about -0.10 to -0.16 V. Only some elements interfere with Bi, such as arsenic, mercury, copper, and antimony. Copper interferes at high concentrations and is separated by extraction [101]. Arsenic or antimony in urine are oxidized to their pentavalent states [125]. 

The glass tubes contain mercury and are firmly fixed in the ebonite cover of the cell so that the distance between the electrodes may not change during the experiment. Contact with the platinum electrodes is made by dipping the copper wires of the circuit in the mercury contained in the tubes. The coating of the electrodes with platinum black is carried out in order to inhibit polarization. When examining certain electrolytes, platinized electrodes cannot be used since platinum black may catalyze the decomposition or the oxidation of the electrolyte. The cell is maintained at constant temperature thermostatically, as conductivity increases rather significantly with temperature. 

Platinum electrodes used in Method 101.4 (Ref 10a, pi) are wires 0,0l6-inch diam, sealed-in-glass, with mercury connections. A magnetic stirrer with plastic- or glass-coated stirring bar is used (See Fig 6) for stirring the liquid in the cell. The cell is emptied by means of a glass suction tube and a suitable trap connected to a vacuum line... 

Note that the metal does not dissolve in the solution. An electrode of this type, which is often used because of its stability, is the calomel electrode shown in Fig. 4. This consists of a platinum wire inserted into liquid mercury, which is coated with mercurous chloride. The electrode reaction is... 

The conductance cells different in shape which are illustrated in Fig. 4. are of glass or quartz two exactly parallel electrodes made of thick platinum sheet (in order to keep Constant their mutual position) are dipped into the cells. To suppress the polarization phenomena the electrodes are coated with platinum black. The current is fed through glass tubes filled with mercury the connections of the electrodes are sealed in the glass at the bottom of the tubes while at the top lead-in wires are immersed in the mercury for connection with the terminals of the measuring instruments. 

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