Coulometry stripping currents

In the previous chapter, we encountered a form of coulometry known as stripping . We can combine both stripping and voltammetry in the powerful technique of stripping voltammetry. As we have seen, the potential of the working electrode is ramped during a voltammetric or polarographic experiment. The resultant current represents the rate at which electroactive analyte reaches the surface of the electrode, that is, current / a flux j. 

In the event that current integration equipment is not available, it is still possible to conduct a quality coulometry experiment by observing the decay of the electrolysis current with time as suggested by MacNevin and Baker [71]. The electrolysis current can be monitored by using a simple strip-chart recorder or a personal computer (PC) equipped with a simple analog-to-digital (A/D) conversion board. Equation 3.49 can be rewritten as... 

In the conductivity, potentiometric, and voltam-metric measurements the response is correlated to concentration or activity of the analyte usually by using calibration curves. In coulometry, however, the charge measured gives directly the amount of substance and therefore no calibration is needed. However, in coulometry the sample is consumed in the measurements and the problem is that the method requires 100% current efficiency to be reliable. Conductimetry and potentiometry are sample nonconsuming methods. In voltammetry, only an insignificant amount of the sample is consumed and therefore the measurement can be repeated. Only in voltammetric stripping methods of very low concentrations of the analyte the amount consumed at the electrode reaction has to be considered if repeated measurements are to be done. 

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