Zeta Potential In View of Pharmaceutical Development

 Zeta potential is a scientific term for electrokinetic potential in colloidal systems1. It means the potential difference existing between the surface of a solid particle immersed in a conducting liquid and the bulk of the liquid2. Zeta potential is important for understanding the stability of colloidal dispersions, such as multivitamin syrups3.

Zeta potential can be used to develop pharmaceutically stable, flocculated suspensions4. Flocculation is the process of forming loose clusters of particles that can be easily separated from a liquid. Zeta potential can be influenced by factors such as electrolyte concentration, pH, and surface charge of the particles5. By adjusting these factors, one can achieve optimal flocculation and prevent unwanted aggregation or sedimentation.

Zeta potential has also been applied to develop a diagnostic system for blood-cell agglutination testing based on the principles of zeta potential4. Agglutination is the clumping of blood cells due to antibodies or other substances. Zeta potential can help measure the degree of agglutination and identify blood types or diseases.

There are different methods for measuring zeta potential, but one of the most common and convenient ones is laser Doppler velocimetry (LDV)1. This method uses a laser beam to measure the velocity of particles moving under an applied electric field.

To measure zeta potential using LDV, you need a device called a zeta potential analyzer23. This device has a disposable folded capillary cell that holds your sample. The cell has two electrodes that apply an electric field across the sample. The device also has a laser source and a detector that measure the Doppler shift of the scattered light from the moving particles.

The zeta potential analyzer calculates the zeta potential based on the electrophoretic mobility of the particles, which is proportional to their velocity and inversely proportional to their size and viscosity of the liquid21. The device can also measure other parameters such as pH, conductivity, and temperature that may affect zeta potential.

This is how you can measure zeta potential using LDV. 

Electrophoretic mobility is a measure of how fast a particle moves under an electric field. It depends on the size, shape, charge, and viscosity of the particle and the liquid1.

There are different theoretical models that link electrophoretic mobility with zeta potential1. One of the most widely used ones is the Henry equation2:

zeta = u * eta / (epsilon * f(ka))

where

• zeta is the zeta potential in volts
• u is the electrophoretic mobility in m^2 / (V * s)
• eta is the dynamic viscosity of the liquid in Pa * s
• epsilon is the dielectric constant of the liquid in F / m
• f(ka) is a dimensionless function that depends on ka, which is a parameter related to the thickness of the electric double layer around the particle

The function f(ka) can be approximated by different expressions depending on the value of ka. For example, if ka > 6, then f(ka) = 1.5. If 0.1 < ka < 6, then f(ka) = 1 + (2/3) * ka + (0.41 - 0.25 * ka) / ka^3. If ka < 0.1, then f(ka) = 1 + ka.

This is how you can calculate zeta potential from electrophoretic mobility using Henry equation.