Isoelectric Point (IEP) Test








Zeta potential is a measure of the charge on the surface of a particle. The zeta potential is a function of the specific surface chemistry of a dispersion and is affected by changes in pH, salt and surfactant concentration. The isoelectric point (IEP) is the pH value at which the zeta potential value is zero, implying no electric charge on the surface of a particle (droplet, molecule, etc.).  Determining the IEP of a dispersion can be helpful to predict stability/instability and to identify the predominant chemical species on the surface of an engineered particle.

IEP tests are helpful in the following situations:

  • Predicting optimum conditions for dispersion stability
  • Determining the predominant chemical species on the surface of complex particles
  • The IEP of proteins is important for storage stability and in processes including gel electrophoresis

The IEP can be measured using the Nicomp 380 ZLS by titrating the sample and measuring the zeta potential as a function of pH.  Two examples of IEP measurements made on the Nicomp 380 ZLS include an emulsion (CoffeMate) and a protein (bovine serum albumin).