Phase Analysis Light Scattering Zeta Potential Analyzer

What is the Phase Analysis Light Scattering Zeta Potential Analyzer?

A zeta potential analyzer using phase analysis light scattering (PALS) to measure very small electrophoretic mobilities. It gives reliable results in high-conductivity or near-isoelectric samples, non-aqueous media and low electric fields, where classical Doppler methods lose signal quality.

Overview

PALS tracks the phase of the scattered light relative to the reference beam over time, which is far more sensitive to slow particle motion than the frequency shift measured by classical laser Doppler electrophoresis. This allows low applied fields, reducing heating, electrode polarisation and sample degradation, and makes it possible to measure mobilities near zero at the isoelectric point. Instruments of this type are suited to high-conductivity buffers up to about 200 mS/cm, to hydrocarbons and alcohols with low dielectric constants, and to proteins in physiological media. Field-reversal sequences combine fast and slow reversal to separate electro-osmotic flow from true mobility. Sample volume is typically 0.75 mL in a disposable capillary cell, with temperature control from 0 to 90 °C.

How does it work?

Charged particles in a liquid are surrounded by an electrical double layer. The zeta potential is the potential at the slipping plane of this layer, and cannot be measured directly. Electrophoretic light scattering applies an electric field and measures particle velocity from the Doppler shift of scattered laser light; electrophoretic mobility is then converted to zeta potential by the Smoluchowski or Hückel approximation, or the Henry function for intermediate cases. Phase analysis light scattering improves sensitivity by measuring phase rather than frequency shift. Streaming potential instruments force electrolyte through a capillary or plug and measure the generated potential difference for solids. Electroacoustic methods detect sound waves generated by an applied alternating field in concentrated suspensions. Key components include the laser, electrodes and cell, temperature control and often a titrator.

What are the key features?

• Phase analysis light scattering detection for near-zero mobility
• Low-field operation to limit heating and electrode reactions
• Fast and slow field reversal for electro-osmosis correction
• Operation in buffers up to about 200 mS/cm
• Non-aqueous solvent capability with dielectric constant input
• Disposable capillary cells with gold-plated electrodes

What are the technical specifications?

A typical phase analysis light scattering zeta potential analyzer configuration offers mobility range of ±20 µm·cm/V·s, mobility sensitivity of ≤ 0.005 µm·cm/V·s, zeta potential range of −500 to +500 mV, measurement principle of PALS with field reversal, laser of 633 nm or 660 nm, ≥ 10 mW and applied field of Low-field, 5–20 V/cm. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Phase Analysis Light Scattering Zeta Potential Analyzer is used in protein and monoclonal antibody formulation, samples near the isoelectric point, high-salt buffers and physiological media, non-aqueous dispersions in oils and alcohols and liposome and lipid nanoparticle studies. Across the wider Zeta Potential Analyzers class, laboratories also deploy it for colloidal stability of emulsions and suspensions, protein and biologic formulation screening and water and wastewater coagulation control.

Which standards and certifications apply?

Relevant standards and methods include ISO 13099-1, ISO 13099-2, ISO 13099-3, ASTM D4187, GB/T 32671 and ISO 13320. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Zeta potential depends on pH, ionic strength, temperature and sample history, so each report should state dispersant, pH, conductivity and temperature. Use low-conductivity, filtered dispersants and avoid bubbles at the electrodes; high salt can cause electrode polarisation and sample heating. Verify performance periodically using a zeta potential transfer standard, typically around −42 mV, and follow the supplier's interval. Clean cells thoroughly, since contamination and electrode degradation alter results. Gold or palladium electrodes and disposable capillary cells simplify maintenance. For regulated use, carry out IQ/OQ/PQ and maintain audit trails. Report the model used to convert mobility to zeta potential.

How do I select the right Phase Analysis Light Scattering Zeta Potential Analyzer?

Select PALS when samples have low mobility, high salt or low dielectric constant solvents, or when heating must be minimised, as in biologics and non-aqueous formulations. Specify conductivity range, solvent dielectric constants, sample volume limits, pH titration needs and compliance software. For simple dilute aqueous colloids, the standard electrophoretic variant is usually sufficient.

How does it compare with other Zeta Potential Analyzers variants?

Begin with the sample type. Dilute colloids and macromolecules suit electrophoretic light scattering; very low-mobility or high-conductivity samples benefit from phase analysis light scattering. Concentrated opaque suspensions, such as slurries, need electroacoustic methods, and flat or fibrous solids need streaming potential. If isoelectric point or pH dependence is required, choose a system with an automatic titrator. Check the required size range, conductivity limits, minimum sample volume and whether non-aqueous solvents are used, since the dielectric constant must be known. Decide if zeta potential alone is enough or whether combined size measurement is needed. Also weigh software validation support, cell durability and cost of disposable cells, and whether ISO 13099 conformity is expected in your methods.