Controlled potential methods electrogravimetric

There is a whole gamut of electrochemical methods available for the determination of the transition elements. Electrogravimetric methods are available for large numbers of metals (e.g. Cu, Ag, Cd, Co, Ni, Sn, Zn, Pb, and Tl) provided these are available in weighable amounts. Controlled potential electrolysis at a mercury pool electrode is best suited for separations (e g. Cu, Cd, and Pd from uranium) or removing traces of metalUc impurities when preparing very pure electrolytes for use in polarography. ... 

Electrolysis at controlled potential can also serve as an elegant method of removing interfering metals from samples to be analyzed by other methods such as spectrophotometry or polarography. The electrogravimetric and coulometric procedures mentioned above represent such separations. The electrolysis can, however, be carried out primarily as a selective separation, with the actual determination being... 

There are two general types of electrogravimetric methods. In one, no control of the potential of the working electrode is exercised, and the applied cell potential is held at a more or less constant level that provides a large enough current to complete the electrolysis in a reasonable length of time. The second type of electrogravimetric method is the controlled-potential or potentiostatic method. 

Table 22-2 lists some other separations performed by controlled-potential electrolysis. Because of limited sensitivity and the time required for washing, drying, and weighing the electrodes, many electrogravimetric methods have been replaced by the coulometric methods discussed in the next section. 

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