For Organic colloids & ^Fe/_Al hydrous oxides

The organic colloids consist of convoluted chains and rings of carbon atoms bonded to hydrogen, oxygen and nitrogen.
For organic colloids and ^Fe/_Al hydrous oxides, ZPC = isoelectric point.
ZPC is the point of zero charges and is described as the pH at which the net charge of the total particle surface is equal to zero. And the isoelectric charge is the pH at which a particular molecule carries no net electrical charge.