The Fitness for Purpose of Analytical Methods

The Fitness for Purpose of Analytical Methods
A Laboratory Guide to Method Validation and Related Topics

Contents
Foreword to the second edition ……………………………………………………………………………………. 1
Foreword to the first edition ……………………………………………………………………………………….. 2
Abbreviations and symbols ………………………………………………………………………………………….. 3
1 Introduction ………………………………………………………………………………………………………… 5
1.1 Rationale and scope for this Guide ………………………………………………………………………….. 5
1.2 Notes on the use of this Guide …………………………………………………………………………………. 5
1.2.1 Terminology …………………………………………………………………………………………………………………….. 5
1.2.2 Quick References ……………………………………………………………………………………………………………… 6
2 What is method validation? ………………………………………………………………………………….. 7
2.1 Definitions ……………………………………………………………………………………………………………… 7
2.2 What is the difference between validation and verification? …………………………………….. 7
3 Why is method validation necessary? …………………………………………………………………….. 9
3.1 Importance of analytical measurement ……………………………………………………………………. 9
3.2 The professional duty of the analytical chemist ………………………………………………………… 9
3.3 Method development ………………………………………………………………………………………………. 9
4 When should methods be validated or verified? ……………………………………………………. 11
4.1 Method validation…………………………………………………………………………………………………. 11
4.2 Method verification ………………………………………………………………………………………………. 11
5 How should methods be validated? ……………………………………………………………………… 13
5.1 Who carries out method validation? ………………………………………………………………………. 13
5.1.1 Approaches to method validation ………………………………………………………………………………………..13
5.1.2 Interlaboratory approach ……………………………………………………………………………………………………13
5.1.3 Single-laboratory approach ………………………………………………………………………………………………..13
5.2 Extent of validation studies …………………………………………………………………………………… 13
5.3 Validation plan and report ……………………………………………………………………………………. 14
5.4 Validation tools …………………………………………………………………………………………………….. 15
5.4.1 Blanks……………………………………………………………………………………………………………………………..15
5.4.2 Routine test samples ………………………………………………………………………………………………………….15
5.4.3 Spiked materials/solutions ………………………………………………………………………………………………….15
5.4.4 Incurred materials ……………………………………………………………………………………………………………..15
5.4.5 Measurement standards ……………………………………………………………………………………………………..15
5.4.6 Statistics ………………………………………………………………………………………………………………………….16
5.5 Validation requirements ……………………………………………………………………………………….. 16
5.6 Method validation process …………………………………………………………………………………….. 16
6 Method performance characteristics ……………………………………………………………………. 19
6.1 Selectivity …………………………………………………………………………………………………………….. 19
6.1.1 Terms and definitions ………………………………………………………………………………………………………..19
6.1.2 Effects of interferences ………………………………………………………………………………………………………19
6.1.3 Assessment of selectivity …………………………………………………………………………………………………..19

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6.2 Limit of detection and limit of quantification …………………………………………………………. 20
6.2.1 Terms and definitions ………………………………………………………………………………………………………..20
6.2.2 Determination of the standard deviation at low levels ……………………………………………………………21
6.2.3 Estimating LOD ……………………………………………………………………………………………………………….24
6.2.4 Estimating LOQ ……………………………………………………………………………………………………………….24
6.2.5 Alternative procedures ………………………………………………………………………………………………………25
6.2.6 Capability of detection for qualitative analysis ……………………………………………………………………..25
6.3 Working range ……………………………………………………………………………………………………… 27
6.3.1 Definition ………………………………………………………………………………………………………………………..27
6.3.2 Considerations for the validation study ………………………………………………………………………………..27
6.3.3 Method and instrument working range…………………………………………………………………………………27
6.3.4 Assessing instrument working range ……………………………………………………………………………………27
6.3.5 Assessing method working range ………………………………………………………………………………………..28
6.4 Analytical sensitivity …………………………………………………………………………………………….. 30
6.4.1 Definition ………………………………………………………………………………………………………………………..30
6.4.2 Applications …………………………………………………………………………………………………………………….30
6.5 Trueness ………………………………………………………………………………………………………………. 30
6.5.1 Terminology to describe measurement quality ……………………………………………………………………..30
6.5.2 Determination of bias ………………………………………………………………………………………………………..31
6.5.3 Interpreting bias measurements …………………………………………………………………………………………..34
6.6 Precision ………………………………………………………………………………………………………………. 35
6.6.1 Replication ………………………………………………………………………………………………………………………35
6.6.2 Precision conditions ………………………………………………………………………………………………………….35
6.6.3 Precision limits …………………………………………………………………………………………………………………36
6.6.4 Simultaneous determination of repeatability and intermediate precision …………………………………..36
6.7 Measurement uncertainty ……………………………………………………………………………………… 38
6.8 Ruggedness …………………………………………………………………………………………………………… 38
6.8.1 Definition ………………………………………………………………………………………………………………………..38
6.8.2 Ruggedness test ………………………………………………………………………………………………………………..38
7 Using validated methods …………………………………………………………………………………….. 41
8 Using validation data to design quality control …………………………………………………….. 43
8.1 Introduction …………………………………………………………………………………………………………. 43
8.2 Internal quality control …………………………………………………………………………………………. 43
8.3 External quality control ………………………………………………………………………………………… 44
9 Documentation of validated methods …………………………………………………………………… 45
9.1 From draft to final version ……………………………………………………………………………………. 45
9.2 Recommendations ………………………………………………………………………………………………… 45
9.2.1 Checking the instructions …………………………………………………………………………………………………..45
9.2.2 Recommendations in standards …………………………………………………………………………………………..45
9.2.3 Document control ……………………………………………………………………………………………………………..45
10 Implications of validation data for calculating and reporting results…………………… 47
Annex A – Method documentation protocol ……………………………………………………………….. 49
Annex B – Statistical basis of limit of detection calculations ………………………………………… 53
Annex C – Analysis of variance (ANOVA) …………………………………………………………………. 54
Annex D – Notes on qualitative analysis …………………………………………………………………….. 56
Bibliography ……………………………………………………………………………………………………………. 59