ZETA POTENTIAL AND COLLOID CHEMISTRY Eric

The US Food and Drug Administration often requests the measurement of zeta potential; however, there is virtually no guidance offered in any of the regulatory pharmacopoeias. Guidelines are available in other standards, and there exists a wealth of information in texts and publications. Many of these are taken from non-pharmaceutical industries where zeta potential is routinely used as part of quality control criteria. This discussion outlines current guidance to aid quality units with potential issues and questions; reviews the complex topics of colloid chemistry and zeta potential; and provides insight to chemists who may require zeta potential determination, but who may not be well versed in these topics. Basic colloid principles are discussed including definitions, types of colloidal systems, and common properties. Types of colloidal particles, micelles, and surrounding layers are detailed. Colloidal stability is discussed. Electrokinetic effects and underlying theories by which electrophoretic mobility is used to calculate zeta potential are detailed. Sample preparation, the importance of sample history, determination of zeta potential, and isoelectric point measurement are discussed.