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Short answer: zeta potential is the electrical potential at the slipping (shear) plane of a particle moving in a liquid, measured relative to the bulk liquid. It is reported in millivolts (mV) and is usually measured by electrophoretic light scattering on an instrument such as a Zetasizer. It describes the particle and its medium together, not the particle alone.
This page is for researchers and lab staff who need to read, report or sanity-check a zeta potential value. It is general technical information about a laboratory measurement.
What does the term zeta potential mean?
A charged particle in a liquid attracts a layer of counter-ions, and the whole assembly moves together when an electric field is applied. The zeta potential is the potential at the slipping plane, the boundary between liquid that travels with the particle and liquid that does not, relative to the bulk liquid (Malvern Panalytical; nanoComposix, both read 2026-11-07).
Two consequences matter in practice. First, it is not a direct measure of surface charge: it also depends on surface composition, ion adsorption, double-layer thickness and molecules attached to the surface (nanoComposix). Second, it belongs to the system. Malvern Panalytical states that the concentration of ions, the types of ions and the pH all affect the zeta potential, so the same particles in a different medium give a different value.
What are the units for zeta potential?
Zeta potential is expressed in millivolts (mV) (Malvern Panalytical, read 2026-11-07). The instrument measures electrophoretic mobility under an applied field, and the zeta potential is then calculated from the mobility using a model, so the reported mV value depends on the model chosen.
What instrument measures zeta potential, and how is it checked?
Malvern Panalytical describes the standard approach as electrophoretic light scattering (ELS), also called laser Doppler velocimetry, with its Zetasizer Advance range (Ultra, Pro and Lab) and disposable folded capillary cells. nanoComposix adds that Zetasizer systems use phase analysis light scattering (PALS), including M3-PALS with slow field reversal. Part 2 of ISO 13099, edition 2 (2025), covers optical methods for electrophoretic mobility, namely video microscopy and electrophoretic light scattering including PALS; it is read together with ISO 13099-1, which covers theory.
The conversion from mobility to zeta potential uses a model. nanoComposix gives the Henry relation, UE = 2·ε·ζ·f(κa) / (3·η), with the Smoluchowski limit for thin double layers and the Hückel limit for thick ones.
Sample preparation points from the sources
- About 1 mL of sample is typical for folded-capillary cells (nanoComposix).
- Use a matched, filtered dispersant rather than pure water, and record the pH after dilution.
- Higher ionic strength compresses the double layer and usually lowers the magnitude of the zeta potential.
- Highly conductive samples (above several mS/cm) can be hard to measure in older folded-capillary systems.
- Equilibrate temperature; bubbles and dust disturb the measurement.
Sizing is a separate measurement. See the guide to dynamic light scattering Z-average and PDI, and the guides to cuvettes, pH meters and sonicators for related bench topics.
How do you interpret zeta potential values?
Malvern Panalytical’s stability guide is organised by magnitude, not sign:
| Zeta potential magnitude | Colloid stability behaviour |
|---|---|
| 0 to ±10 mV | Highly unstable; rapid coagulation or flocculation |
| ±10 to ±20 mV | Limited stability |
| ±20 to ±30 mV | Moderately stable |
| Beyond ±30 mV | Highly stable |
The isoelectric point is the pH at which mobility and zeta potential cross zero (nanoComposix).
What a lab should report with a zeta potential value
Because the value depends on conditions, nanoComposix lists the following to record alongside the number. Use it as a reporting checklist:
| Record this | Why it matters (source) |
|---|---|
| Medium / dispersant | Ion types and concentration change the value (Malvern Panalytical; nanoComposix) |
| pH (after dilution) | pH affects the value; dilution can shift it (Malvern Panalytical; nanoComposix) |
| Conductivity | Ionic strength compresses the double layer; very conductive samples are harder to measure (nanoComposix) |
| Temperature | Samples should be equilibrated; heating can cause drift (nanoComposix) |
| Concentration and dilution | Dilution artefacts can change the result (nanoComposix) |
| Model used (Smoluchowski, Hückel, Henry) | The mV value is calculated from mobility via a model (nanoComposix) |
Common misunderstandings
- “It is the particle’s surface charge.” It is the potential at the slipping plane and depends on the medium and surface chemistry (nanoComposix).
- “Sign decides stability.” The stability table is by magnitude, not sign (Malvern Panalytical).
- “Above 30 mV passes, below fails.” nanoComposix cautions that it is not a pass/fail test: sterically stabilised particles (for example PEG-coated) can be stable at low zeta potential, so pair it with sizing such as DLS.
- “The value belongs to the material.” It belongs to the particle in a specific medium and pH.
- “Filtering or centrifuging is harmless.” It can change the population being measured (nanoComposix).
Frequently asked questions
What are the units for zeta?
Millivolts (mV).
What does the term zeta potential mean?
The electrical potential at the slipping plane of a particle in a liquid, relative to the bulk liquid; it reflects the particle and its medium together.
How to check zeta potential?
Measure electrophoretic mobility under an applied field in a matched dispersant at recorded pH, conductivity and temperature, then convert it with a stated model. See the preparation points above.
What instrument measures zeta potential?
An electrophoretic light scattering instrument, for example the Malvern Panalytical Zetasizer Advance range, using disposable folded capillary cells.
Sources
- Malvern Panalytical, zeta potential measurement type page: https://www.malvernpanalytical.com/en/products/measurement-type/zeta-potential (read 2026-11-07).
- nanoComposix, zeta potential measurements: https://nanocomposix.com/pages/zeta-potential-measurements (read 2026-11-07).
- ISO 13099-2:2025, Colloidal systems: Methods for zeta-potential determination, Part 2: Optical methods (edition 2, August 2025); read with ISO 13099-1 (theory). Title and edition cited from catalogue listings, 2026-11-07.
