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Faster, More Sensitive Zeta-Potential Measurements with cmPALS and the Litesizer™ 500

In this application report we describe a newly patented technology termed cmPALS, which is incorporated in the Litesizer™ 500 particle analyzer. cmPALS results in a dramatic enhancement of the sensitivity and stability of zeta-potential measurements. We first present some background information about the technical development of cmPALS, then we compare the ELS performance of the cmPALS instrument (the Litesizer™ 500) to that of a PALS instrument.

Zeta potential is 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, where particles will tend to aggregate or coagulate. Thus, knowledge of zeta potential is important for optimizing manufacturing processes and for quality control.

Zeta potential measurements require the application of an electric field to the sample. But since electric fields can lead to Joule heating and sample degradation, the electric fields must 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 the so-called Phase-Analysis Light Scattering (PALS), which is based on electrophoretic light scattering (ELS). PALS was an improvement over previous ELS methods because it no longer required the application of large electric fields, so Joule heating was reduced. However, PALS measurements have proved somewhat unreliable, especially for sensitive samples requiring very short measuring times and low electric fields. 

Here we present our patented Continuously-Monitored Phase-Analysis Light Scattering (cmPALS, patent EP2735870), a development of the PALS technology that enables the Litesizer™ 500 to perform ELS with increased sensitivity and stability. For the user, this means significantly shorter measurement times and lower applied electric fields, so that sensitive samples can be analyzed with confidence. 

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