Current-potential curves recommendations

Polarography and Voltammetry Both methods are the same in that current-potential curves are measured. According to the IUPAC recommendation, the tenn polarography is used when the indicator electrode is a liquid electrode whose surface is periodically or continuously renewed, like a dropping or streaming mercury electrode. When the indicator electrode is some other electrode, the term voltammetry is used. However, there is some confusion in the use of these terms. 

The starting potential should be located at a potential where no current flows through the working electrode. Often this potential can be determined as the open circuit or rest potential of the solution. This ensures that the current/potential curve starts at i = 0. The initial condition of homogeneous distribution of the redox active species throughout the electrolyte is fulfilled. If this precaution is not taken, the product of the electron transfer is produced at the electrode before the start of the scan and diffuses towards the bulk electrolyte. Consequently, some distortion of the voltammetric curve may be observed. In practical terms, the recommended... 

Majer65 in 1936 proposed measuring, instead of the entire polarographic curve, only the limiting current at a potential sufficiently high for that purpose if under these conditions one titrates metal ions such as Zn2+, Cd2+, Pb2+, Ni2+, Fe3+ and Bi3+ with EDTA66, one obtains a titration as depicted in Fig. 3.55 i, decreases to a very low value, in agreement with the stability constant of the EDTA-metal complex and the titration end-point is established by the intersection of the ij curves before and after that point correction of the i values for alteration of the solution volume by the titrant increments as in conductometric titration is recommended. 

The increase of clock time at a properly chosen pulse amplitude and scan rate does not effect the peak current or the peak potential seriously. The curves are smoothed as T decreases (v and AE fixed) and can consequently be evaluated more precisely. In spite of this a time T = 1.0 is recommended, because the complete decay of the reverse current spike due to the potential step back to the actual dc potential disturbes less the current sample before the application of the next potential pulse, as can be seen in Table 1. The thickness of the spacer does not have any greater effect on the measured dpv current. 

At the recommended potential, Pb give a diffusion current. The titration curve resembles an... 

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