An Application Report from Anton Paar introduces the use of newly patented technology cmPALS in its Litesizer 500 particle-analyser.
cmPALS (Continuously Monitored Phase-Analysis Light Scattering) results in dramatic enhancements in the sensitivity and stability of zeta-potential measurements. The report first describes some background information about the technical
development of cmPALS and then presents a direct comparison of results from the cmPALS instrument with those from a PALS instrument. To compare their performance, the zeta potential of a latex standard (0.05 % in 10 mM NaCl) was measured with both methods.
Zeta potential is a key indicator of colloid stability. The higher the magnitude of the zeta potential, 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.
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, but this can lead to sample heating and decomposition. Electric fields must
therefore be kept as low as possible, and applied for as short a time 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. Measurements can, however, be unreliable, especially with sensitive samples, where very short measuring times and low electric fields are required.
