Particle size analysis — Laser diffraction methods

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).

Analyse granulométrique — Méthodes par diffraction laser

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Publication Date
05-Jan-2020
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6060 - International Standard published
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06-Jan-2020
Completion Date
06-Jan-2020
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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)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2020 – All rights reserved
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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

© ISO 2020 – All rights reserved iii
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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

iv © ISO 2020 – All rights reserved
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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.
© ISO 2020 – All rights reserved v
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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.
vi © ISO 2020 – All rights reserved
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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.
© ISO 2020 – All rights reserved 1
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ISO 13320:2020(E)
[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

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;

n is the positive real part of the refractive index of a particle.

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’)
2 © ISO 2020 – All rights reserved
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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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ISO 13320:2020(E)
[SOURCE: ISO 3534-2:2006, 3.3.4]
3.1.16
reference material

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
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;
n is the complex refractive index of a particle.
See single scattering (3.1.26).
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ISO 13320:2020(E)
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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ISO 13320:2020(E)
3.1.28
test sample
sample that is entirely used for a property characterization
[SOUR
...

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