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Controlled potential coulometry digital prediction of endpoints

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  • In 19589 J. J. Lingane published an article describing the behavior of an electrolysis using controlled potential coulometry. A typical titration was an hour or more, limiting the variety of applications of the technique. Stephens, Jakob, Rigdon and Harrar looked into the many procedures that have been proposed to locate the electrolysis endpoint without carrying it to completion. Unfortunately, the extrapolation techniques, when used off-line, shorten the electrolysis time only at the expense of operator time, and they generally sacrifice accuracy." In their article, the Stephens research team propose a real time computer technique that determines the endpoint of the electrolysis while it is being carried out. In their technique, they utilize a total accumulated charge signal that is proportional to the amount of electroactive species that has been titrated. This signal is obtained by electronically integrating the cell current signal. By predicting the total charge signal at infinite time (Qoo). the original concentration of electroactive species can be determined. In the course of the mathematics involved in this prediction, the background current of the cell must be considered. The method the Stephens team used was to incorporate the background current into the error term used in the prediction. This method has its strong points and the results have as small as .02% relative error. It is the purpose of this paper to look into some alternate real time computer techniques of determining the initial concentration of the electroactive species using the cell current signal instead of total accumulated charge, and attempting to eliminate the background current from the data itself.
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