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Navigating murky waters: a breakthrough in measuring Zeta potential of turbid and concentrated samples

The Litesizer™ 500 benefits from the patented cmPALS technology, a further development of the popular PALS method for ELS, which results in a dramatic enhancement of the sensitivity and stability of zeta potential measurements. Anton Paar’s Omega cuvette is a folded capillary cell with a particularly narrow sample channel, which minimizes the likelihood of multiple scattering events. Here we demonstrate that the zeta potential of turbid and highly concentrated samples can be measured accurately and reliably using the Litesizer™ 500 and the Omega cuvette. Comparable measurements made on a conventional, PALS-based instrument with standard zeta potential cuvettes were markedly more inaccurate.

Zeta potential measurements are a convenient way to determine the stability of colloids against aggregation. In order for colloidal particles to remain in suspension, they must repel each other, or else they will cluster together and undergo sedimentation. For particles to repel each other, they need to have a certain surface charge, which is reflected in their zeta potential.

Zeta potential can be determined by electrophoretic light scattering (ELS), in which the electrophoretic mobility is measured and then used to calculate the zeta potential. In a typical optical configuration, the light scattered by the particles is detected in the forward angle (15°), which means the laser beam must travel through the whole sample. This is problematic for concentrated samples, because the light is likely to be scattered by more than one particle on its path through the sample. As calculation of the zeta potential relies on the light only being scattered once, such multiple scattering leads to an inaccurate zeta potential. Therefore, zeta potential cannot usually be accurately measured on turbid or highly concentrated samples.

The Omega cuvettes produced by Anton Paar have been specially designed to circumvent that problem. Their sample channel is particularly narrow, which means that the path length of the laser through the sample is relatively short, thereby minimizing the chance of multiple scattering events. In addition, the Litesizer™ 500 benefits from our patented cmPALS technology, which significantly improves the sensitivity of the zeta potential measurements compared to PALS-based instruments.

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