Titrators, automatic working electrode

Figure 11 -5 shows an autotitrator, which performs the entire operation automatically.4 Titrant from the plastic bottle at the rear is dispensed in small increments by a syringe pump while pH is measured by electrodes in the beaker of analyte on the stirrer. (We will learn how these electrodes work in Chapter 15.) The instrument waits for pH to stabilize after each addition, before adding the next increment. The end point is computed automatically by finding the maximum slope in the titration curve. 

In addition, further errors can be made in titration procedures which are purely chemical or physico-chemical in origin. Supersaturation effects can sometimes be observed. This arises when for short periods of time the solution contains more ions than it should on the basis of the solubility product of the corresponding precipitate. i>e-cipitate formation, and thus the electrode EMF, is a time-dependent process (such as the titration of traces of fluoride with a lanthanum solution. Fig. 50). For this reason caution is required when working with automatic titration devices. 

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