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Technical
Specification
ISO/TS 5973
First edition
Laser diffraction measurements —
2024-07
Good practice
Mesures par diffraction laser — Bonnes pratiques
Reference number
© ISO 2024
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Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 4
5 Laser diffraction experiment and measurement . 4
6 Information recommended collecting prior to analysis . 5
6.1 Sample information .5
6.2 Desired outcome of analysis . .6
6.3 Other sample considerations .7
6.4 Best sampling practice prior to laser diffraction measurements .8
6.4.1 General .8
6.4.2 Sampling of powders .8
6.4.3 Sampling of emulsions and suspensions .9
6.4.4 Sampling of sprays, gas bubbles and aerosols .9
6.4.5 Improving sampling in the instrument .10
7 Samples not appropriate for analysis by laser diffraction .10
8 Additional guidance on optical properties of samples .11
8.1 Coloured samples .11
8.2 Porous samples .11
8.3 Mixtures .11
8.4 Mie, Fraunhofer and incorrect use of refractive index .11
9 Repeatability, intermediate precision and reproducibility .12
9.1 General . 12
9.2 Key measurands . 12
9.3 Instrument repeatability . 12
9.4 Method repeatability (under repeatability conditions) . 13
9.5 Intermediate precision and reproducibility (under intermediate precision/
reproducibility conditions).14
9.6 Summary table of experiments detailed in 9.3 through 9.5 . 15
9.7 When is tighter or wider control needed? . 15
9.8 What are the most appropriate control parameters? . 15
10 Interpretation of light scattering and assessment of data quality .15
10.1 Background stability and alignment quality . 15
10.2 Multiple scattering .16
10.3 Non-smooth scattering patterns .16
11 Interpretation of trends in measurement data .16
11.1 General .16
11.2 Dispersion (wet measurements) .16
11.3 Dissolution (wet measurements) .17
11.4 Agglomeration (wet measurements) .17
11.5 Size decreasing on successive measurements (dry measurements) .17
11.6 Random variation (wet measurements) .17
11.7 Other causes of poor repeatability (wet and dry measurements).17
12 Orthogonal techniques for laser diffraction .18
12.1 Image analysis.18
12.2 Dynamic light scattering .18
iii
13 Validation, installation qualification, operational qualification and performance
qualification . 19
Annex A (informative) Characterization data approach to laser diffraction measurements .20
Bibliography .23
iv
Foreword
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v
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 because 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
are available. Nevertheless, the proper use of the instrument and the interpretation of the results require
caution. ISO 13320 has had multiple revisions to date and covers the principles of the technology and
information on evaluating the accuracy of the instrument with a view to qualification. ISO 13320 does not,
however, cover the use of the technology on samples in great detail, and therefore, this document is intended
to be used in conjunction with ISO 13320, as this document provides practical advice for the measurement of
real samples, guidance on obtaining consistent results with good quality data and data interpretation.
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Technical Specification ISO/TS 5973:2024(en)
Laser diffraction measurements — Good practice
1 Scope
This document gives guidance on the determination criteria for when laser diffraction is the most
appropriate method for the analysis of samples, the appropriate preparation of samples, the verification of
the correct functioning of instruments, the interpretation of data, and the assessment of data
...