White Paper: cmPALS: The New Standard in Zeta Potential Analysis
Zeta potential is a key parameter for the investigation of colloid stability. Electroosmosis and sample degradation must be counteracted during the measurements in order to prevent errors in the zeta potential results. The main electrophoretic light scattering based techniques PALS and cmPALS offer two different approaches to solve these drawbacks. The physical principles behind PALS and cmPALS are described and compared in the following article.
Zeta potential is a measure of the surface charge or surface functionalities and a key indicator of colloid stability. The higher the magnitude of the zeta potential (that is, highly positive or highly negative), the more stable the colloid. A lower-magnitude zeta potential indicates a less stable colloid; in other words, the colloidal particles will tend to aggregate or coagulate. Thus, knowledge of zeta potential is important for optimizing processes and for quality control. Nonetheless, the measurement of zeta potential has previously been beset by significant limitations. Zeta potential measurements require an electric field to be applied to the sample. However, electric fields can lead to sample heating and decomposition, so the electric fields must be kept as low as possible, and be applied for as short as possible. Until now, the state of the art in zeta-potential measurements was phase-analysis light scattering (PALS), which is based on electrophoretic light scattering (ELS) measurements. PALS was an improvement over previous ELS measurements, because it no longer required the application of such large fields, so sample heating and decomposition was reduced. PALS measurements can be unreliable, however, especially when testing sensitive samples, where very short measuring times and low electric fields are required. We describe herein the patented technology called cmPALS (EP2735870), which is incorporated in the particle analyzer Litesizer 500. cmPALS leads to a significant enhancement in sensitivity and stability of zeta-potential measurements. In the first part of this article some background information about the technical development of cmPALS is described, before a direct comparison of results obtained from the Litesizer 500 which uses cmPALS with those from an instrument using the conventional PALS instrument is presented. In the end, few application examples for zeta potential will be also discussed.
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