ISO 13320:2020

INTERNATIONAL ISO
STANDARD 13320
Second edition
2020-01
Particle size analysis — Laser
diffraction methods
Analyse granulométrique — Méthodes par diffraction laser
Reference number
ISO 13320:2020(E)
©
ISO 2020

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ISO 13320:2020(E)

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© ISO 2020
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Published in Switzerland
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ISO 13320:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 6
4 Principle . 8
4.1 General . 8
4.2 Theory . 8
4.3 Typical instrument and optical arrangement. 9
4.4 Measurement zone .11
4.5 Application and sample presentation .11
4.6 Off-line measurements .12
4.7 In-line measurements .12
4.8 Online measurements .12
4.9 At-line measurements .13
4.10 Scattering and detectors .13
5 Operational requirements and procedures .13
5.1 Instrument location .13
5.2 Dispersion gases .13
5.3 Dispersion liquids .14
5.4 Sample inspection, preparation, dispersion and concentration .14
5.4.1 Sample inspection .14
5.4.2 Preparation .14
5.4.3 Dispersion .14
5.4.4 Concentration .15
5.5 Measurement .15
5.5.1 Setting up instrument and blank measurement .15
5.5.2 Sample preparation .16
5.5.3 Data collection of the scattering pattern .16
5.5.4 Selection of an appropriate optical model .16
5.5.5 Conversion of scattering pattern into PSD .16
5.5.6 Robustness .17
5.6 Resolution and sensitivity .17
5.6.1 General.17
5.6.2 Resolution .17
5.6.3 Sensitivity and result variability .17
6 Accuracy repeatability and instrument qualification.18
6.1 General .18
6.2 Accuracy .19
6.2.1 Introduction .19
6.2.2 Accuracy test .19
6.3 Instrument repeatability .19
6.3.1 Introduction .19
6.3.2 Repeatability test .19
6.4 Method repeatability .20
6.4.1 Introduction .20
6.4.2 Method repeatability test .20
6.5 Accuracy under intermediate precision conditions .20
6.5.1 General.20
6.5.2 Intermediate precision conditions (general test) .21
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ISO 13320:2020(E)

7 Reporting of results .21
7.1 General .21
7.2 Sample .21
7.3 Dispersion .22
7.4 Laser diffraction measurement .22
7.5 Analyst identification: .22
Annex A (informative) Theoretical background of laser diffraction .24
Annex B (informative) Advice on dispersion liquids .41
Annex C (informative) Dispersion methods — Recommendations .42
Annex D (informative) Instrument preparation — Recommendations .44
Annex E (informative) Error sources and diagnosis .46
Annex F (informative) Refractive index — Recommendations .49
Annex G (informative) Laser diffraction robustness and ruggedness .51
Annex H (normative) Certified reference materials, reference materials and comparison
parameters .54
Bibliography .57
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ISO 13320:2020(E)

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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
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 13320:2009), which has been technically
revised. The main changes compared to the previous edition are as follows:
a) protocols for evaluation of accuracy and qualification of instrument were newly developed;
b) new Annex H (normative) for usage of reference material has been added;
c) new descriptions for wider applications, such as off-line, online, in-line and at-line have been added;
d) some informative parts have been moved to new annexes;
e) minor revisions and updates have been made throughout the document.
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.
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ISO 13320:2020(E)

Introduction
The laser diffraction technique has evolved such that it is now a dominant method for determination
of particle size distributions (PSDs). The success of the technique is based on the fact that it can be
applied to a wide variety of particulate systems. The technique is fast and can be automated, and a
variety of commercial instruments is available. Nevertheless, the proper use of the instrument and the
interpretation of the results require the necessary caution.
Since ISO 13320-1:1999 was first published, the understanding of light scattering by different materials
and the design of instruments have advanced considerably. This is especially marked in the ability
to measure very fine particles. Therefore, it was replaced with the first edition of ISO 13320 in 2009,
and since then the method has been developed for a wider application. Additionally, demands raised
recently not only on establishment of accuracy of measurements but also on necessity of evaluation
of the accuracy and of qualification of instrument by users. Therefore, this document incorporates the
most recent advances in understanding.
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INTERNATIONAL STANDARD ISO 13320:2020(E)
Particle size analysis — Laser diffraction methods
1 Scope
This document provides guidance on instrument qualification and size distribution measurement of
particles in many two-phase systems (e.g. powders, sprays, aerosols, suspensions, emulsions and gas
bubbles in liquids) through the analysis of their light-scattering properties. It does not address the
specific requirements of particle size measurement of specific materials.
This document is applicable to particle sizes ranging from approximately 0,1 µm to 3 mm. With special
instrumentation and conditions, the applicable size range can be extended above 3 mm and below 0,1 µm.
For spherical and non-spherical particles, a size distribution is reported, where the predicted scattering
pattern for the volumetric sum of spherical particles matches the measured scattering pattern. This
is because the technique assumes a spherical particle shape in its optical model. For non-spherical
particles the resulting particle size distribution is different from that obtained by methods based on
other physical principles (e.g. sedimentation, sieving).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 9276-1, Representation of results of particle size analysis — Part 1: Graphical representation
ISO 9276-2, Representation of results of particle size analysis — Part 2: Calculation of average particle
sizes/diameters and moments from particle size distributions
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1.1
absorption
reduction of intensity of a light beam not due to scattering
3.1.2
accuracy
closeness of agreement between a test result or measurement result and the true value
Note 1 to entry: In practice, the accepted reference value is substituted for the true value.
Note 2 to entry: The term “accuracy”, when applied to a set of test or measurement results, involves a combination
of random components and a common systematic error or bias component.
Note 3 to entry: Accuracy refers to a combination of trueness and precision.
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[SOURCE: ISO 3534-2:2006, 3.3.1]
3.1.3
aspect ratio
ratio of the minimum to the maximum Feret diameter
Note 1 to entry: For not very elongated particles.
[SOURCE: ISO 26824:2013, 4.5]
3.1.4
certified reference material
CRM
reference material (3.1.16) characterised by a metrologically valid procedure for one or more specified
properties, accompanied by an RM certificate that provides the value of the specified property, its
associated uncertainty, and a statement of metrological traceability
Note 1 to entry: The concept of value includes a nominal property or a qualitative attribute such as identity or
sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence.
Note 2 to entry: Metrologically valid procedures for the production and certification of RMs are given in, among
others, ISO 17034 and ISO Guide 35.
Note 3 to entry: ISO Guide 31 gives guidance on the contents of RM certificates.
Note 4 to entry: ISO/IEC Guide 99:2007, 5.14 has an analogous definition.
[SOURCE: ISO Guide 35:2017, 3.2]
3.1.5
complex refractive index
n
p
refractive index of a particle, consisting of a real and an imaginary (absorption) part
Note 1 to entry: The complex refractive index of a particle can be expressed mathematically as
   n = n − ik
p p p
where
i is the square root of −1;
k is the positive imaginary (absorption) part of the refractive index of a particle;
p
n is the positive real part of the refractive index of a particle.
p
Note 2 to entry: In contrast to ISO 80000-7, this document follows the convention of adding a minus sign to the
imaginary part of the refractive index.
3.1.6
deconvolution
mathematical procedure whereby the size distribution of an ensemble of particles is
inferred from measurements of their scattering pattern
3.1.7
diffraction
scattering of light around the contour of a particle, observed at a substantial
distance (in the ‘far field’)
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ISO 13320:2020(E)

3.1.8
equivalent spherical diameter
particle size reported from a distribution of spherical particles that creates a
scattering pattern that matches the light scattering distribution observed from the measurement
Note 1 to entry: The scattering pattern of the spherical particles is calculated according to an optical model.
3.1.9
extinction
attenuation of a light beam traversing a medium through absorption and
scattering
3.1.10
intermediate precision
accuracy and precision under intermediate precision conditions (3.1.11)
[SOURCE: ISO 3534-2:2006, 3.3.15, modified — field of application has been added.]
3.1.11
intermediate precision conditions
conditions where test results or measurement results are obtained on different
laser diffraction instruments and with different operators using the same prescribed method
Note 1 to entry: There are four elements to the operating condition: time, calibration, operator and equipment.
3.1.12
multiple scattering
consecutive scattering of light by more than one particle, causing a scattering pattern that is no longer
the sum of the patterns from all individual particles
3.1.13
obscuration
fraction of incident light that is attenuated due to extinction (scattering and/or absorption) by particles
Note 1 to entry: Obscuration can be expressed as a percentage.
Note 2 to entry: When expressed as fractions, obscuration plus transmission (3.1.29) equal unity.
[SOURCE: ISO 8130-13:2019, 3.1, modified — words “percentage” and “during a laser diffraction
measurement” have been omitted because of context.]
3.1.14
optical model
theoretical model used for computing the model matrix for optically homogeneous and isotropic
spheres with, if necessary, a specified complex refractive index
EXAMPLE Fraunhofer diffraction model, Mie scattering model.
3.1.15
precision
closeness of agreement between independent test/measurement results obtained under stipulated
conditions
Note 1 to entry: Precision depends only on the distribution of random errors and does not relate to the true value
or the specified value.
Note 2 to entry: The measure of precision is usually expressed in terms of imprecision and computed as a
standard deviation of the test results or measurement results. Less precision is reflected by a larger standard
deviation.
Note 3 to entry: Quantitative measures of precision depend critically on the stipulated conditions. Repeatability
conditions and reproducibility conditions are particular sets of extreme stipulated conditions.
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[SOURCE: ISO 3534-2:2006, 3.3.4]
3.1.16
reference material
RM
material, sufficiently homogeneous and stable with respect to one or more specified properties, which
has been established to be fit for its intended use in a measurement process
Note 1 to entry: RM is a generic term.
Note 2 to entry: Properties can be quantitative or qualitative, e.g. identity of substances or species.
Note 3 to entry: Uses may include the calibration of a measurement system, assessment of a measurement
procedure, assigning values to other materials, and quality control.
Note 4 to entry: ISO/IEC Guide 99:2007 has an analogous definition but restricts the term “measurement” to
apply to quantitative values. However, ISO/IEC Guide 99:2007, 5.13, Note 3 (VIM), specifically includes qualitative
properties, called “nominal properties”.
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.17
reflection
change of direction of a light wave at a surface without a change in wavelength
or frequency
3.1.18
refraction
process by which the direction of a radiation is changed as a result of changes in its velocity of
propagation in passing through an optically non-homogeneous medium, or in crossing a surface
separating different media
Note 1 to entry: The process occurs in accordance with Snell's law:
   n sinθ = n sinθ
m m p p
See 3.2 for symbol definitions.
3.1.19
relative refractive index
m
rel
ratio of the complex refractive index of a particle to the real part of the dispersion medium
[SOURCE: ISO 24235:2007, 3.3, modified — “absolute refractive index” has been replaced by “complex
refractive index” and “the sample” has been replaced by “a particle”.]
Note 1 to entry: In many applications, the medium is transparent and, thus, its refractive index has a negligible
imaginary part.
Note 2 to entry: The relative refractive index can be expressed mathematically as
    m = n /n
rel p m
where
n is the real part of the refractive index of the medium;
m
n is the complex refractive index of a particle.
p
See single scattering (3.1.26).
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3.1.20
repeatability
precision under repeatability conditions (3.1.21)
Note 1 to entry: Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the
results.
[SOURCE: ISO 3534-2:2006, 3.3.5]
3.1.21
repeatability conditions
observation conditions where independent test/measurement results are obtained with the same
method on identical test/measurement items in the same test or measuring facility by the same
operator using the same equipment within short intervals of time
Note 1 to entry: Repeatability conditions include:
— the same measurement procedure or test procedure;
— the same operator;
— the same measuring or test equipment used under
— the same conditions;
— the same location;
— repetition over a short period of time.
[SOURCE: ISO 3534-2:2006, 3.3.6]
3.1.22
method repeatability
closeness of agreement between multiple measurement results of a given property in different aliquots
of a sample, executed by the same operator using the same instrument under identical conditions
within a short period of time
Note 1 to entry: The variability includes the variabilities of sub sampling technique, of the sampled material
together and of the instrument.
3.1.23
scattering
change in propagation of light at the interface of two media having different optical properties
3.1.24
scattering angle
angle between the principal axis of the incident light beam and the scattered light
3.1.25
scattering pattern
angular pattern of light intensity, I(θ), or spatial pattern of light intensity, I(r), originating from
scattering, or the related energy values taking into account the sensitivity and the geometry of the
detector elements
3.1.26
single scattering
scattering whereby the contribution of a single member of a particle population to the total scattering
pattern remains independent of the other members of the population
3.1.27
single shot
for an analysis, for which the entire content of a test sample container is used
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3.1.28
test sample
sample that is entirely used for a property characterization
[SOUR
...