Outlining Zeta Potential Measurements
Zeta potential measurements are a common protocol when analyzing colloidal systems (beverages, food, inks, paints, pharmaceuticals, etc.). It is a complex parameter that defines the electro-kinetic potential of heterogeneous liquids, typically formulations comprising microscopic/nanoscale insoluble particles dispersed in a mobile phase. The sheer breadth of that definition indicates how complex zeta potential measurements can be, and the broad range of application areas open to instruments concerned with colloidal electro-kinetics.
In this blog post, Particulate Systems offers a brief overview of zeta potential and outlines some of the instruments that we offer for high-precision zeta potential measurements.
What is Zeta Potential?
Zeta potential (ζ) is a key property in microfluidics. Depending on the measurement scale, it is either expressed in terms of volts (V) or millivolts (mV). It is concerned with the solid-liquid interface of dispersive particles within a mobile phase, where negatively- and positively-charged ions form an electrical double layer (DL); parallel charge layers that encompass the particle. Zeta potential measurements are concerned with the differential attraction/repulsion between the dispersive and that of this interfacial double layer.
Why Perform Zeta Potential Measurements?
This differential is indicative of short- and long-term colloidal stability, allowing formulators to predict the shelf-life of colloidal systems with respect to various aggregating phenomena. There is no general rule expressing an ideal electrical surface charge for all colloidal systems, however, studies have shown an ideal range for the dispersion of nanoparticles in a mobile phase. Nanoparticle colloids with a zeta potential approaching zero are more prone to destabilizing particle migration phenomena. This is associated with shorter shelf-lives and often poor product quality.
Zeta potential measurements that indicate an electrical differential greater than 30mV – whether positively or negatively charged – typically indicate longer colloidal stability and reduced proclivity towards particle aggregation.
Applications of Zeta Potential Measurements
We offered a brief overview of some of the main sectors that routinely conduct zeta potential measurements in the introduction, but it is worth exploring this in more depth to gain a practical insight into the theory of colloidal electro-kinetics. One of the most common applications of zeta potential measurements is shelf-life forecasting, and research and development (R&D) of new and optimized formulations. This area straddles various markets, from the food and beverage sector, where extending product shelf-lives is critical in improving product ROIs, to pharmaceuticals, where poor electro-kinetics may indicate bad batches and subsequent regulatory non-compliance.
Zeta Potential Measurements with Particulate Systems
Particulate Systems supplies the Zetasizer Nano Family for zeta potential measurements and molecular characterization of colloidal systems in a wide range of market sectors. Both the Zetasizer Nano ZS and Zetasizer Nano S offer two distinct methods of light scattering analysis: dynamic light scattering (DLS), and electrophoretic light scattering (ELS). The ELS method is key for zeta potential measurements as it assesses electrophoretic mobility of nanoparticles in solution by applying an electrical field to the system and observing the velocity of particles migrating towards oppositely-charged electrodes. This is easily converted into a zeta potential measurement for accurate insight into the aggregating behavior of various colloids.Posted on