Determination of Isoelectric point

The isoelectric point (pI) is the pH of a solution at which the net charge of a zwitterion molecule (e.g. amino acids, peptides, proteins) becomes zero. At solution pH that is above the pI, the surface of the molecule is predominantly negatively charged, while it becomes positively charged when the solution pH is lower than the pI.

Identifying the isoelectric point of your molecule can help in several ways:

• For protein purification, where proteins have minimal water solubility at their pI.
• Study the best level of outer charge for your application

How it is done

The determination of isoelectric point is done through measurment of the zeta potential of your molecules / particles at a series of pH points, and finding the point where it the zeta potential value becomes zero.

Measurements are done on the Nanosizer device (Malvern, UK) available at Nawah.