Standard
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AS/NZS ISO 33405:2024
[Current]Reference materials - Approaches for characterization and assessment of homogeneity and stability
AS/NZS ISO 33405:2024 identically adopts ISO 33405:2024, which explains concepts and provides approaches to the following aspects of production of reference materials (RMs): assessment of homogeneity; assessment of stability and management of risks associated with possible stability issues related to properties of interest; characterization and value assignment of properties of RM; evaluation of uncertainty for certified values; and establishment of metrological traceability of certified values
Published: 30/08/2024
Pages: 103
Table of contents
Cited references
Content history
Table of contents
Header
About this publication
Preface
Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Conventions
6 Overview of reference material production
6.1 General
6.2 Summary of project design
6.3 Acquisition of starting material
6.4 Feasibility studies
6.5 Reference material processing
6.6 Homogeneity assessment
6.7 Stability assessment
6.8 Choice of measurement procedures
6.9 Metrological traceability
6.10 Characterization and uncertainty evaluation
6.11 Commutability assessment
6.12 Transport issues
6.13 Value assignment
6.14 Stability monitoring
6.15 Reference materials produced in repeated batches
7 Assessment of homogeneity
7.1 Preamble
7.2 Need for an experimental homogeneity study
7.3 Properties to be studied
7.4 Statistically valid sampling schemes
7.4.1 Minimum number of units for a homogeneity study
7.4.1.1 Homogeneity study for quantitative properties
7.4.1.2 Homogeneity study for qualitative (“nominal”) properties
7.4.1.3 Small production batches
7.4.2 Use of statistical power analysis
7.4.3 Sampling strategies for a homogeneity study
7.5 Choice and conduct of the measurement procedure for a homogeneity study
7.5.1 Choice of measurement procedure
7.5.2 Conduct of measurements for homogeneity studies
7.6 Homogeneity study designs
7.6.1 Objective of a homogeneity study
7.6.2 The basic homogeneity study design – measurement in a single run
7.6.3 Randomized block design
7.6.4 Balanced nested design
7.6.5 Alternative strategies
7.7 Evaluating a homogeneity study
7.7.1 Initial inspection for measurement trends and outliers
7.7.1.1 Measurement trends
7.7.1.2 Outliers in the basic homogeneity study
7.7.2 Inspection for processing trends
7.7.3 Evaluation of the between-unit term – basic design
7.7.4 Evaluation of the between-unit term – randomized block design
7.7.5 Evaluation of the between-unit term – balanced nested design
7.7.6 Other homogeneity designs and alternative estimation methods
7.8 Insufficient repeatability of the measurement procedure
7.9 Within-unit homogeneity
7.9.1 Assessing the need for within-unit homogeneity study
7.9.2 Testing for significant within-unit heterogeneity
7.9.3 Assessing minimum sample size
7.9.3.1 Experimental determination
7.9.3.2 Other methods
7.10 Check for sufficient homogeneity
7.11 Uncertainty evaluation from homogeneity studies
8 Assessment and monitoring of stability
8.1 Preamble
8.2 Assessment of stability
8.2.1 Requirement for stability assessment
8.2.2 Types of (in)stability
8.2.3 General methods for assessment of stability
8.2.4 Need for experimental study of stability
8.2.4.1 General requirements on the need for experimental study of stability
8.2.4.2 Need for experimental study of stability in repeated batch production
8.3 Classification of stability studies
8.3.1 General
8.3.2 Classification according to conditions of measurement
8.3.2.1 Classical stability studies – Intermediate conditions of measurement
8.3.2.2 Isochronous stability studies – Repeatability conditions of measurement
8.3.3 Classification according to stability study duration and conditions
8.3.3.1 Real-time stability studies
8.3.3.2 Accelerated stability studies
8.3.4 Classification by study objective
8.3.4.1 Transportation or other short-term stability studies
8.3.4.2 Long-term stability studies
8.3.5 Designs for different storage and treatment conditions
8.4 General requirements for effective stability studies
8.4.1 Overview of requirements
8.4.2 Selection of RM units
8.4.3 Suitable measurement procedure(s) for stability studies
8.4.4 Appropriate experimental design
8.5 Evaluation of stability study results
8.5.1 General considerations for stability study data treatment
8.5.2 The basic stability study: multiple points in time at a single storage condition
8.5.2.1 Applicability
8.5.2.2 Procedure
8.5.2.3 Model selection
8.5.2.4 Fitting the model
8.5.2.5 Inspection and check of assumptions
8.5.2.6 Testing for significant instability
8.5.3 Isochronous designs
8.5.3.1 Simple isochronous study with one storage and one reference condition
8.5.3.2 Advantages and disadvantages of isochronous stability studies
8.5.3.3 Extensions of the basic isochronous design
8.5.4 Accelerated stability studies with multiple exposure conditions
8.5.4.1 Description of accelerated studies
8.5.4.2 Mathematical models for assessing accelerated stability studies
8.5.4.3 Advantages and disadvantages of accelerated stability studies
8.5.5 Additional sources of random variation in stability studies
8.6 Action on finding a significant trend in a stability study
8.7 Uncertainty evaluation from stability studies
8.7.1 General considerations for uncertainty evaluation from stability studies
8.7.2 Sources of uncertainty in predicted change over time
8.7.3 Estimation of stability uncertainties in the absence of significant trends
8.7.4 Evaluation of stability uncertainties in the case of a known significant trend
8.8 Estimation of storage lifetime (“shelf life”) from a stability study
8.9 Instructions for use related to management of stability
8.10 Stability monitoring
8.10.1 Requirements for monitoring
8.10.2 Choice of initial monitoring point and monitoring interval(s)
8.10.2.1 Relevance of prior information
8.10.2.2 Monitoring plans where extensive prior information is available
8.10.2.3 Monitoring plans where extensive prior information is not available
8.10.2.3.1 General considerations for monitoring where prior information is not available
8.10.2.3.2 Use of a predicted change to set the initial monitoring point
8.10.2.3.3 Use of a simple multiple of the stability study duration
8.10.3 Experimental approaches and evaluation for stability monitoring
8.10.3.1 Classical monitoring design
8.10.3.2 Evaluation of stability monitoring results
8.10.3.3 Isochronous stability monitoring
9 Characterization of the material
9.1 Preamble
9.2 Establishing metrological traceability
9.2.1 Principle
9.2.2 Metrological references
9.2.3 Types of measurands
9.2.4 Effect of sample preparation or pre-treatment
9.2.5 Verification of traceability
9.3 Characterization using a single reference measurement procedure (as defined in ISO/IEC Guide 99) in a single laboratory
9.3.1 Characterization by a reference measurement procedure without direct comparison with a CRM of the same kind
9.3.1.1 Concept
9.3.1.2 Measurement procedure requirements
9.3.2 Characterization by value transfer from a reference material to a closely matched candidate reference material using a single measurement procedure performed by one laboratory
9.3.2.1 Principle
9.3.2.2 Assigned value and uchar
9.3.2.3 Traceability
9.3.3 Selection of RM units for single-laboratory characterization
9.3.4 Formulation methods
9.4 Characterization of a non-operationally defined measurand using two or more methods of demonstrable accuracy in one or more competent laboratories
9.4.1 Concept
9.4.1.1
9.4.1.2
9.4.1.3
9.4.1.4
9.4.2 Study design
9.4.3 Evaluation
9.4.3.1 Technical and statistical evaluation
9.4.3.2 Assigned value and uncertainty
9.4.4 Single-laboratory multi-method studies
9.5 Characterization of an operationally defined measurand using a network of competent laboratories
9.5.1 Concept
9.5.2 Study setup
9.5.3 Evaluation
9.6 Purity
9.6.1 General
9.6.2 Direct determination of purity
9.6.3 Indirect determination of purity
9.7 Ordinal scales
9.8 Nominal properties including identity
9.9 Characterization of non-certified values
10 Evaluating measurement uncertainty
10.1 Basis for evaluating the uncertainty of a property value of a CRM
10.2 Basic model for a batch characterization
10.3 Uncertainty sources
10.4 Coverage intervals and factors
Annex A
A.1 Study design
A.1.1 Selection of measurement procedures
A.1.2 Choice of calibration standards
A.1.3 Selection of laboratories
A.1.4 Number of independent data sets
A.1.5 Number of RM units and replicate determinations
A.1.6 Quality control materials
A.1.7 Instructions for participants
A.1.8 Reporting
A.2 Evaluation
A.2.1 General considerations for evaluation
A.2.2 Initial screening
A.2.2.1 General
A.2.2.2 Technical evaluation
A.2.3 Statistical evaluation
A.2.3.1 General principles for statistical evaluation
A.2.3.2 Distributions
A.2.3.3 Outliers
A.2.3.4 Robust statistics
A.2.3.5 Grouping (“clustering”)
A.2.4 Assigned value (weighted or unweighted mean)
A.2.5 Assigned uncertainty
A.2.5.1 Use of analysis of variance for uncertainty evaluation
A.2.5.2 Uncertainty-based evaluation
A.2.5.3 Evaluation without the laboratories' uncertainties
A.3 Use of collaborative studies for multiple purposes
A.3.1
A.3.2
A.3.3
Annex B
B.1 One-way analysis of variance
B.2 Two-way analysis of variance for nested designs
B.3 Linear regression (univariate linear model)
B.3.1 The basic model
B.3.2 Fitting the model
B.3.3 Inspection and check of assumptions
B.3.4 Testing for statistically significant change
B.3.5 Confidence interval for the regression line
B.4 Predicting lifetime or choosing initial monitoring point based on stability study results
B.4.1 Principle
B.4.2 Prediction of lifetime in the case of a linear trend
B.4.3 Prediction of lifetime for other degradation models
B.4.4 Choosing an initial monitoring point
B.5 Robust statistics
B.5.1 Robust estimators for interlaboratory studies
B.5.2 Evaluation of uncertainties for robust estimators
Annex C
C.1 Homogeneity study
C.2 Between-unit homogeneity, considering the limited repeatability of the measurement procedure
C.3 Homogeneity assessment using a randomized block design
C.3.1 Background and data
C.3.2 Evaluation
C.4 Homogeneity assessment: simple design with correction for linear trend
C.4.1 Background and data
C.4.2 Method 1: correction for trend followed by classical analysis of variance
C.4.3 Method 2: incorporating the run trend in the analysis
Annex D
Bibliography
Cited references in this standard