Pristine point of zero charge PPZC

The PZC is usually measured in the presence of electrolytes. In many cases, one or both of the ions can adsorb on the surface. The PZC is then dependent on both the proper surface properties and also the content of the dispersion medium. If the medium does not contain any ions which specifically adsorb on the surface, the PZC is only dependent on the material in the colloidal particles. Such a PZC is known as a pristine point of zero charge (PPZC) (see Table 1.1). 

These measurements allow the determination of the IBP, and because no reference is needed in this technique, finally the pristine point of zero charge of a sorbent sample is obtained. Although information on charge at a certain distance from the particle surface is not really available, the pH, at which the particles do not move in an appUed field (or where the potential difference measured is zero), is an indication for the absence of charge on the probe particles. This particular pH is called the lEP. If the lEP coincides for different values of ionic strength and with a correctly determined CIP, this pH can be identified as the PPZC (at least of the sample). The relative charge obtained in a titration can then be renormalized to absolute charge. 

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