ISO 22412:2017

INTERNATIONAL ISO
STANDARD 22412
Second edition
2017-02
Particle size analysis — Dynamic light
scattering (DLS)
Analyse granulométrique — Dispersion lumineuse dynamique (DLD)
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 3
5 Principle . 4
6 Apparatus . 5
7 Test sample preparation . 7
7.1 General . 7
7.2 Concentration limits . 7
7.3 Checks for concentration suitability. 7
8 Measurement procedure . 8
9 Evaluation of results .10
9.1 General .10
9.2 Correlation analysis .11
9.2.1 Cumulants method .11
9.2.2 Distribution calculation algorithms .11
9.3 Frequency analysis .12
10 System qualification and quality control .13
10.1 System qualification .13
10.2 Quality control of measurement results .13
10.3 Method precision and measurement uncertainty .14
11 Test report .14
Annex A (informative) Theoretical background .16
Annex B (informative) Guidance on potential measurement artefacts and on ways to
minimize their influence .25
Annex C (informative) Online measurements .28
Annex D (informative) Recommendations for sample preparation .29
Bibliography .33
Foreword
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This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition of ISO 22412 cancels and replaces ISO 22412:2008 and ISO 13321:1996.
iv © ISO 2017 – All rights reserved

Introduction
Particle size analysis in the submicrometre size range is performed on a routine basis using the dynamic
light scattering (DLS) method, which probes the hydrodynamic mobility of the particles. The success of
the technique is mainly based on the fact that it provides estimates of the average particle size and
size distribution within a few minutes, and that user-friendly commercial instruments are available.
Nevertheless, proper use of the instrument and interpretation of the result require certain precautions.
Several methods have been developed for DLS. These methods can be classified in several ways:
a) by the difference in raw data acquisition (autocorrelation, cross-correlation and frequency
analysis);
b) by the difference in optical setup (homodyne versus heterodyne mode);
c) by the angle of observation.
In addition, instruments show differences with respect to the type of laser source and often allow
application of different data analysis algorithms (e.g. cumulants, NNLS, CONTIN, etc.).
INTERNATIONAL STANDARD ISO 22412:2017(E)
Particle size analysis — Dynamic light scattering (DLS)
1 Scope
This document specifies the application of dynamic light scattering (DLS) to the measurement of average
hydrodynamic particle size and the measurement of the size distribution of mainly submicrometre-
sized particles, emulsions or fine bubbles dispersed in liquids. DLS is also referred to as “quasi-elastic
light scattering (QELS)” and “photon correlation spectroscopy (PCS),” although PCS actually is one of
the measurement techniques.
This document is applicable to the measurement of a broad range of dilute and concentrated
suspensions. The principle of dynamic light scattering for a concentrated suspension is the same as
for a dilute suspension. However, specific requirements for the instrument setup and specification of
test sample preparation are required for concentrated suspensions. At high concentrations, particle-
particle interactions and multiple light scattering can become dominant and can result in apparent
particle sizes that differ between concentrated and dilute suspensions.
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 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:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary can also be described as an interface.
Note 2 to entry: A particle can move as a unit.
[SOURCE: ISO 26824:2013, 1.1, modified]
3.2
average hydrodynamic diameter
x
DLS
hydrodynamic diameter that reflects the central value of the underlying particle size distribution
Note 1 to entry: The average particle diameter is either directly determined without calculation of the particle
size distribution, or calculated from the computed intensity-, volume- or number-weighted particle size
distribution or from its fitted (transformed) density function. The exact nature of the average particle diameter
depends on the evaluation algorithm.
Note 2 to entry: The cumulants method yields a scattered light intensity-weighted harmonic mean particle
diameter, which is sometimes also referred to as the “z-average diameter.”
Note 3 to entry: Arithmetic, geometric and harmonic mean values can be calculated from the particle size
distribution according to ISO 9276-2.
Note 4 to entry: Mean values calculated from density functions (linear abscissa) and transformed density
functions (logarithmic abscissa) may significantly differ (ISO 9276-1).
Note 5 to entry: x also depends on the particle shape and the scattering vector (and thus on the angle of
DLS
observation, laser wavelength and refractive index of the suspension medium).
3.3
polydispersity index
PI
dimensionless measure of the broadness of the size distribution
Note 1 to entry: The PI typically has values less than 0,07 for a monodisperse test sample of spherical particles.
3.4
scattering volume
volume defined by the intersection of the incident laser beam and the scattered light intercepted by the
detector
3.5
scattered intensity
intensity of the light scattered by the particles in the scattering volume
3.6
count rate
photocurrent
I
s
number of photon pulses per unit time
Note 1 to entry: It is also a photodetector current which is proportional to the scattered intensity as measured
by a detector.
3.7
validation
proof with reference material that a measurement procedure is acceptable for all elements of its scope
Note 1 to entry: Evaluation of trueness requires a certified reference material.
3.8
reference material
RM
material, sufficiently homogeneous and stable with respect to one or more specified pro
...