Simplification of Zeta Potential Measurement through M3-PALS

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Simplification of Zeta Potential Measurement through M3-PALS 

Introduction

  Zeta potential is a measurement of the degree of repulsion or attraction between particles and is considered an important parameter in various industries such as brewing, ceramics, pharmaceuticals, and water treatment.
However, measuring zeta potential can be complex and requires some level of expertise to obtain accurate and reliable results. Malvern Instruments has not only simplified zeta potential measurement through the new Zetasizer Nano series but also improved measurement accuracy by utilizing a new measurement technology called M3 PALS.

  Understanding the zeta potential of dispersions allows for the control of electrostatic interactions of the dispersion, thus controlling the stability of emulsions or dispersions. This can be crucial for efficacy, shelf life, and product performance.

  Over the past 20 years, awareness of the importance of zeta potential has increased and the available technologies and devices have greatly improved. However, several issues remain such as ease of use of the instruments and cross-contamination of samples within the system itself.

  The Zetasizer Nano system addresses these issues by measuring zeta potential using M3 PALS technology. This is a next-generation technique that combines the patented Mixed Mode Measurement (M3) technique with the established Phase Analysis Light Scattering (PALS). The combination of these techniques makes measurements more accurate and simpler, enabling the development of the world’s first disposable cell for zeta potential measurement that eliminates cross-contamination.

PALS

  PALS is a variant of Laser Doppler Velocimetry (LDV). LDV utilizes a classical electrophoretic cell in which a potential is applied and measures particle mobility based on changes in the frequency of light scattered by particles moving through the cell. The measured mobility is converted to zeta potential using established theories. This technique requires the application of a high electro-field, which can cause thermal problems for highly conductive samples.

  PALS is a much more sensitive technique because it determines frequency changes using information contained within the light scattering phase. While the optical setup is the same as the LDV method, it uses a different signal processing method. The measured phase shift is directly proportional to the change in particle position. Using phase allows for resolution identification about a thousand times greater than that of frequency analysis.

  The PALS technique was originally developed to enhance measurement sensitivity to low mobility samples when the electrophoretic mobility is below the common level of 10-8m2/sV in aqueous media. This technique is generally applied using sinusoidal electric fields through simple parallel plate electrodes, and is particularly useful in distinguishing electrophoretic mobility and thermal fluctuations when achieving temperature stability is challenging due to Joule heating.

M3 Measurement Technique-1

  M3 is a relatively new technique that measures zeta potential utilizing electrophoresis within a capillary cell. By combining the highest measurement capability at stationary level (described below) with the recently proposed Fast Field Reversal (FFR) technique (described below), it enables unprecedented accuracy and resolution.

  When exposed to an electric field, ultrafine particles with very low inertia reach terminal velocity in microseconds. The actual velocity is determined by the charge associated with the particles (zeta potential), the viscosity of the medium, and the applied electric field.

 

Figure 1] Capillary cell showing the location of the stationary layer