ISO 13099-2:2025
(Main)Colloidal systems — Methods for zeta-potential determination — Part 2: Optical methods
Colloidal systems — Methods for zeta-potential determination — Part 2: Optical methods
This document specifies two methods of measurement of the electrophoretic mobility of particles suspended in a liquid: video microscopy and electrophoretic light-scattering. NOTE Estimation of surface charge and determination of zeta-potential can be achieved from measured electrophoretic mobility using proper theoretical models, which are described in detail in ISO 13099-1.
Systèmes colloïdaux — Méthodes de détermination du potentiel zêta — Partie 2: Méthodes optiques
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International
Standard
ISO 13099-2
Second edition
Colloidal systems — Methods for
2025-08
zeta-potential determination —
Part 2:
Optical methods
Systèmes colloïdaux — Méthodes de détermination du
potentiel zêta —
Partie 2: Méthodes optiques
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .1
3.2 Symbols .3
4 Principles . 3
5 Microscopic methods. 4
6 Electrophoretic light-scattering (ELS) method . 5
6.1 General .5
6.2 Cell design .5
6.3 Reference beam optical arrangement .6
6.4 Signal processing .8
6.4.1 Spectrum analysis .8
6.4.2 Autocorrelation function .8
6.4.3 Phase analysis light scattering (PALS) .9
6.4.4 Modulated Brownian motion power spectrum method .9
6.5 Determination of electrophoretic mobility .10
7 Calculation of zeta-potential . 10
8 Operational procedures .11
8.1 Requirements .11
8.1.1 Instrument location .11
8.1.2 Dispersion liquids .11
8.1.3 Measurement cell .11
8.1.4 Sample inspection, preparation, dilution, and concentration . 12
8.2 Verification . . 13
8.2.1 Reference materials . 13
8.2.2 Repeatability . 13
8.2.3 Intermediate precision . 13
8.2.4 Trueness . 13
8.3 Sources of measurement error . .14
8.3.1 Contamination of the current sample by the previous sample .14
8.3.2 Inappropriate sample preparation procedure .14
8.3.3 Inappropriate sample .14
8.3.4 Inappropriate liquid medium .14
8.3.5 Poor temperature stabilization .14
8.3.6 Condensation on the illuminated surfaces .14
8.3.7 Particles, fingerprints or scratches on the optical surfaces .14
8.3.8 Too large a potential applied . 15
8.3.9 Incorrect entry of parameters by the operator . 15
8.3.10 Air bubbles . 15
8.3.11 Cell coating damage . 15
8.3.12 Calculating zeta-potential . 15
8.3.13 Sample stability consideration . 15
8.4 Test report . 15
Annex A (informative) Electroosmosis within capillary cells . 17
Bibliography .20
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had notreceived notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 13099-2:2012), which has been technically
revised.
The main changes are as follows:
— addition of new terms and definitions;
— revision of Figure 3, illustrating instrument configuration;
— removal of section on cross-beam optics;
— revision of the description of phase analysis light scattering (PALS);
— addition of information on cell constant.
A list of all parts in the ISO 13099 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Zeta-potential is a parameter that can be used to predict the long-term stability of suspensions and emulsions
and to study surface morphology and adsorption on particles and other surfaces in contact with a liquid.
Zeta-potential is not a directly measurable parameter. It can be determined using appropriate theoretical
models from experimentally determined parameters, such as electrophoretic mobility.
Optical methods, especially electrophoretic light scattering, have been widely used to determine
electrophoretic mobility of particles or macromolecules in suspension or in solution. The purpose of this
document is to provide methods for measuring electrophoretic mobility using optical means and for
calculating zeta-potential.
v
International Standard ISO 13099-2:2025(en)
Colloidal systems — Methods for zeta-potential
determination —
Part 2:
Optical methods
IMPORTANT — This document is to be read in conjunction with ISO 13099-1, which gives a
comprehensive overview of the theory.
1 Scope
This document specifies two methods of measurement of the electrophoretic mobility of particles suspended
in a liquid: video microscopy and electrophoretic light-scattering.
NOTE Estimation
...
International
Standard
ISO 13099-2
Second edition
Colloidal systems — Methods for
zeta-potential determination —
Part 2:
Optical methods
Systèmes colloïdaux — Méthodes de détermination du
potentiel zêta —
Partie 2: Méthodes optiques
PROOF/ÉPREUVE
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .1
3.2 Symbols .3
4 Principles . 3
5 Microscopic methods. 4
6 Electrophoretic light-scattering (ELS) method . 5
6.1 General .5
6.2 Cell design .5
6.3 Reference beam optical arrangement .6
6.4 Signal processing .8
6.4.1 Spectrum analysis .8
6.4.2 Autocorrelation function .9
6.4.3 Phase analysis light scattering (PALS) .9
6.4.4 Modulated Brownian motion power spectrum method .10
6.5 Determination of electrophoretic mobility .10
7 Calculation of zeta-potential . 10
8 Operational procedures .11
8.1 Requirements .11
8.1.1 Instrument location .11
8.1.2 Dispersion liquids .11
8.1.3 Measurement cell .11
8.1.4 Sample inspection, preparation, dilution, and concentration . 12
8.2 Verification . . 13
8.2.1 Reference materials . 13
8.2.2 Repeatability . 13
8.2.3 Intermediate precision . 13
8.2.4 Trueness . 13
8.3 Sources of measurement error . .14
8.3.1 Contamination of the current sample by the previous sample .14
8.3.2 Inappropriate sample preparation procedure .14
8.3.3 Inappropriate sample .14
8.3.4 Inappropriate liquid medium .14
8.3.5 Poor temperature stabilization .14
8.3.6 Condensation on the illuminated surfaces .14
8.3.7 Particles, fingerprints or scratches on the optical surfaces . 15
8.3.8 Too large a potential applied . 15
8.3.9 Incorrect entry of parameters by the operator . 15
8.3.10 Air bubbles . 15
8.3.11 Cell coating damage . 15
8.3.12 Calculating zeta-potential . 15
8.3.13 Sample stability consideration . 15
8.4 Test report . 15
Annex A (informative) Electroosmosis within capillary cells . 17
Bibliography .20
PROOF/ÉPREUVE
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had notreceived notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 13099-2:2012), which has been technically
revised.
The main changes are as follows:
— addition of new terms and definitions;
— revision of Figure 3, illustrating instrument configuration;
— removal of section on cross-beam optics;
— revision of the description of phase analysis light scattering (PALS);
— addition of information on cell constant.
A list of all parts in the ISO 13099 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE
iv
Introduction
Zeta-potential is a parameter that can be used to predict the long-term stability of suspensions and emulsions
and to study surface morphology and adsorption on particles and other surfaces in contact with a liquid.
Zeta-potential is not a directly measurable parameter. It can be determined using appropriate theoretical
models from experimentally determined parameters, such as electrophoretic mobility.
Optical methods, especially electrophoretic light scattering, have been widely used to determine
electrophoretic mobility of particles or macromolecules in suspension or in solution. The purpose of this
document is to provide methods for measuring electrophoretic mobility using optical means and for
calculating zeta-potential.
PROOF/ÉPREUVE
v
International Standard ISO 13099-2:2025(en)
Colloidal systems — Methods for zeta-potential
determination —
Part 2:
Optical methods
IMPORTANT — This document is to be read in conjunction with ISO 13099-1, which gives a
comprehensive overview of the theory.
1 Scope
This document specifies two methods of measurement of the electrophoretic mobility of particles suspended
in a liquid: video microscopy an
...
2024-04-02
ISO/PRF 13099-2:2025(en)
ISO/TC 24/SC 4
Secretariat: BSI
Date: 2025-05-22
Colloidal systems — Methods for zeta-potential determination —
Part 2:
Optical methods
Systèmes colloïdaux — Méthodes de détermination du potentiel zêta —
Partie 2: Méthodes optiques
PROOF
ISO/PRF 13099-2:2025(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO'sISO’s member body in the country of the requester.
ISO Copyright Office copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii
ii
ISO/PRF 13099-2:2025(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 3
4 Principles . 3
5 Microscopic methods . 5
6 Electrophoretic light-scattering (ELS) method . 6
6.1 General . 6
6.2 Cell design . 6
6.3 Reference beam optical arrangement . 7
6.4 Signal processing . 9
6.5 Determination of electrophoretic mobility. 12
7 Calculation of zeta-potential . 12
8 Operational procedures . 13
8.1 Requirements . 13
8.2 Verification . 16
8.3 Sources of measurement error . 17
8.4 Test report . 19
Annex A (informative) Electroosmosis within capillary cells . 21
Bibliography . 25
iii
iii
ISO/PRF 13099-2:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not receivednot received notice of
(a) patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 13099-2:2012), which has been technically
revised.
The main changes are as follows:
— — addition of new terms and definitions;
— — revision of Figure 3Figure 3,, illustrating instrument configuration;
— — removal of section on cross-beam optics;
— — revision of the description of phase analysis light scattering (PALS);
— — addition of information on cell constant.
A list of all parts in the ISO 13099 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
iv
ISO/PRF 13099-2:2025(en)
Introduction
Zeta-potential is a parameter that can be used to predict the long-term stability of suspensions and emulsions
and to study surface morphology and adsorption on particles and other surfaces in contact with a liquid. Zeta-
potential is not a directly measurable parameter. It can be determined using appropriate theoretical models
from experimentally determined parameters, such as electrophoretic mobility.
Optical methods, especially electrophoretic light scattering, have been widely used to determine
electrophoretic mobility of particles or macromolecules in suspension or in solution. The purpose of this
document is to provide methods for measuring electrophoretic mobility using optical means and for
calculating zeta-potential.
v
v
INTERNATIONAL STANDARD ISO 13099-2:2025(en)
Colloidal systems — Methods for zeta-potential determination —
Part 2: Optical methods
Part 2:
Optical methods
IMPORTANT — This document is to be read in conjunction with ISO 13099-1, which gives a
comprehensive overview of the theory.
1 Scope
This document specifies two methods of measurement of the electrophoretic mobility of particles suspended
in a liquid: video microscopy and electrophoretic light-scattering.
NOTE Estimation of surface charge and determination of zeta-potential can be achieved from measured
electrophoretic mobility using proper theoretical models, which are described in detail in ISO 13099-1.
2 Normative references
There are no normative references for this document,
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1.1 3.1.1
Brownian motion
random movement of particles suspended in a liquid caused by thermal movement of medium molecules
3.1.2 3.1.2
cell constant
proportional constant between the applied electric field, either in a constant voltage or a constant current, and
the electric field strength in the measurement zone of the sample cell, which is unique for each cell and can be
obtained by measuring a medium with known conductivity
3.1.3 3.1.3
Doppler shift
change in frequency and wavelength of a wave for an observer moving relative to the source of the wave
ISO/PRF 13099-2:2025(en)
3.1.4 3.1.4
zeta-potential
electrokinetic potential
ζ-potential
ζ
difference in electric potential between that at the slipping plane and that of the bulk liquid
Note 1 to entry: Zeta-potential is expressed in volts.
3.1.5 3.1.5
electroosmosis
motion of liquid through or past a charged surface, e.g. an immobilized set of particles, a porous plug, a
capillary or a membrane, in response to an applied electric field, which is the result of the force exerted by the
applied field on the counter-charge ions in the liquid
3.1.6
Note 1 to entry: A charged surface can include an immobilized set of particles, a porous plug, a capillary or a membrane.
3.1.6
electroosmotic velocity
υeo
uniform velocity of the liquid far from the charged interface
Note 1 to entry: Electroosmotic velocity is expressed in metres per second.
3.1.63.1.7 3.1.7
electrophoretic mobility
μ
electrophoretic velocity per electric field strength
Note 1 to entry: Electrophoretic mobility is positive if the particles move toward lower potential (negative electrode) and
negative in the opposite case.
Note 2 to entry: Electrophoretic mobility is expressed in metres squared per volt second.
3.1.73.1.8 3.1.8
electrophoretic velocity
υ
e
particle velocity during electrophoresis
Note 1 to entry: Electrophoretic velocity is expressed in metres per second.
3.1.83.1.9 3.1.9
intermediate precision
measurement precision under set of intermediate precision conditions of measurement
[SOURCE: ISO/IEC Guide 99:2007, definition 2.23]
3.1.93.1.10 3.1.10
slipping plane
shear plane
abstract plane in the vicinity of the interface between liquid and solid where liquid starts to slide relative to
the surface under influence of a shear stress
ISO/PRF 13099-2:2025(en)
3.1.103.1.11 3.1.11
trueness
closeness of agreement between the average of an infinite number of replicate measured quantity values and
a reference quantity value
[SOURCE: ISO/IEC Guide 99:2007, 3.17]
3.2 Symbols
a particle radius
D diffusion coefficient
E electric field strength
k Boltzmann constant
B
I light intensity
N Avogadro’s number
A
n medium refractive index
Rcap capillary radius
S(ω) frequency power spectrum of scattering
Γ characteristic Lorentzian half peak width
ε medium permittivity
ζ zeta-potential (electrokinetic potential)
η medium viscosity
θ angle between incident light and scattered light
κ reciprocal Debye length
λ wavelength
μ electrophoretic mobility
μ electroosmotic mobility of liquid
eo
ν frequency
ξ angle between scattered light and electric field direction
τ delay time in autocorrelation function
φ volume fraction
ω rotational frequency (= 2πν)
4 Principles
A suspension of particles having a given electrokinetic charge is placed in a cell which has a pair of electrodes
placed some distance apart (see Figure 1Figure 1).). This cell can be in the form of either a cylindrical or
rectangular capillary with electrodes at either end, or a pair of electrodes at a known fixed distance apart that
ISO/PRF 13099-2:2025(en)
are dipped into a cuvette or other vessel. A potential is applied between the electrodes. Due to the process of
electrophoresis, particles carrying a net negative charge are drawn towards the electrode of opposite sign and
vice versa. In addition, if the capillary walls are charged, then an effect called electroosmosis causes the liquid
to stream along the capillary walls. The direction and velocity of this flow depends on the sign and magnitude
of the wall charge. The resulting velocity of the particle in the frame of references associated with the cell is
superposition of the electrophoretic velocity and the velocity of electroosmotic flow. The time taken for the
particle to reach the terminal electrophoretic velocity after the application of the electric field is
...
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