Isoelectric Point

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Related to PH of ZPC: Potential of Zero Charge

isoelectric point

[¦ī·sō·i′lek·trik ′pȯint]
(physical chemistry)
The pH value of the dispersion medium of a colloidal suspension at which the colloidal particles do not move in an electric field.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Isoelectric Point


(point of zero charge), the state of the surface of a body or of a particle in the dispersed phase in contact with an electrolytic solution; it is characterized by an equal number of positive and negative charges in the adsorption layer. Here the zeta potential is equal to zero. Colloidal systems stabilized by electrolytes are unstable at the isoelectric points—that is, they break down as a result of the adhesion of particles in the dispersed phase. The electrically neutral state of amphoteric electrolytes (ampholytes) that contain separate acid and base groups is also called the isoelectric point. A specific pH value corresponds to the isoelectric point of every ampholyte. At the isoelectric point the molecules of ampholyte, like colloidal particles, lose the ability to shift directionally in an electrical field. The swelling, solubility, and viscosity of solutions and many other characteristics of ampholytes, particularly macromolecular ampholytes, assume extreme values as the isoelectric point is approached.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.