TECHNICAL GUIDANCE FOR THE VALIDATION OF METHODS USED BY CHEMICAL LABORATORIES IN THE FOOD, WATER AND RELATED INDUSTRIES

Transcription

1 TECHNICAL GUIDANCE FOR THE VALIDATION OF METHODS USED BY CHEMICAL LABORATORIES IN THE FOOD, WATER AND RELATED INDUSTRIES Approved By: Chief Executive Officer: Ron Josias Senior Manager: Christinah Leballo Author Specialist Technical Committee Members: Food and Water Date of Approval: Date of Implementation: SANAS Page 1 of 9

2 CONTENTS: 1. Purpose and Scope References Definitions Introduction Validation Plan (Huber: 8.3) Implementation, Evaluation, Reporting and Documentation Revalidation Guidelines for Assessors (PALCAN: 8.6)... 9 SANAS Page 2 of 9

3 1. Purpose and Scope The purpose of this document is to provide guidance on method validation as well as guidance to the SANAS Technical Assessors on how to assess method validation. This document contains supplementary guidance to meeting the requirements of ISO/IEC 17025: References SANAS PM SANAS A 01 SANAS TG 26 SANAS TG 28 SANAS TG 41 SANAS Policy Manual References, Acronyms and Definitions Criteria for validation of methods used by chemical laboratories in the coal, oil, petroleum, metals and minerals industry. Guidelines on validation and quality assurance in microbiological testing. Recommended guidelines for the verification and validation of methods in forensic chemistry. ISO/IEC 17025:2005 General Requirements for the Competence of Testing and Calibration Laboratories SANS :2009, Edition 1. Uncertainty of Measurement. Part 3: Guide to the expression of uncertainty in measurement(gum:1995) Eurachem Guide. The Fitness for Purpose of Analytical Methods. A laboratory guide to method validation and related topics. Copyright LGC (Teddington) Ltd 1998 Ludwig Huber, Validation and Qualification in Analytical Laboratories, second edition. Ludwig Huber. Agilent Technologies. Waldbronn, Germany. ( PALCAN Guidance for the Validation of Test Methods. Can-P November Standards Council of Canada. Reagecon. A guide to Method Validation. Copyright by Reagecon diagnostics Ltd Definitions 3.1 Accuracy - The accuracy of an analytical method is the extent to which test results generated by the method and the true value agree. Accuracy can also be described as the closeness of agreement between the value that is adopted, either as a conventional, true, or accepted reference value, and the value found. (Huber: 8.3) 3.2 Bias The tendency of a method towards delivering a result that is skewed from the true value. It is the difference between the experimental mean and the true value and is generated from a total systematic error as contrasted to random error. 3.3 Limit of Detection (LOD) - The lowest concentration of analyte that can be detected but not necessarily quantified under the stated conditions of the test. It is a point at which a measured value is larger than the uncertainty associated with it. (Huber: 8.3). 3.4 Limit of Quantitation - The lowest concentration of analyte that can be determined with acceptable precision (repeatability) and accuracy under the stated conditions of the test. It is also known as the limit of reporting. (Eurachem: 8.1) SANAS Page 3 of 9

4 Figure 1: The Definitions for linearity, working range, LOQ and LOD are displayed (Huber: 8.3) Figure 2: Limit of detection and limit of quantitation via signal to noise ratio. (Huber: 8.3) 3.5 Linearity - Ability of a method to obtain test results proportional to the concentration of the analyte. (Eurachem: 8.1) 3.6 Precision (Random error) - The closeness of agreement between independent test results obtained under stipulated conditions (how close the measured values are to each other). It is usually expressed as the standard deviation or relative standard deviation (co-efficient of variance) and may be a measure of either the degree of reproducibility and/or repeatability. (Eurachem: 8.1) SANAS Page 4 of 9

5 Figure 3: Graphic presentation of the difference between precision and accuracy. (From Repeatability - The closeness of agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement. Note 1: These conditions are called repeatability conditions Note 2: Repeatability conditions include: - the same measurement procedure - the same observer - the same measuring instrument, used under the same conditions - the same location - repetition over a short period of time Note 3: Repeatability may be expressed quantitatively in terms of the dispersion characteristics of the results. (SANS: 8.9) 3.8 Reproducibility - This refers to replicate analysis performed using the same method on identical test items using different analysts and/or instruments and/or laboratories over a longer interval of time. (Eurachem: 8.1) 3.9 Robustness - A measure of an analytical procedure s capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage. (Eurachem: 8.1) 3.10 Ruggedness - A measure of reproducibility of test results under normal, expected operational conditions from laboratory to laboratory and from analyst to analyst. (Huber: 8.3). Note: Intra-laboratory studies can be used to study the behaviour of an analytical process when small changes in the environmental and/or operating conditions are made. (Eurachem: 8.1) 3.11 Selectivity (or Specificity) - The ability of a method to determine accurately and specifically the analyte of interest in the presence of other components in a sample matrix under the stated conditions of the test. (Eurachem: 8.1) 3.12 Sensitivity This is effectively the gradient of the response curve, i.e the change in instrument response, which corresponds to a change in the analyte concentration. (Reagecon: 8.7) 3.13 Recovery - Is expressed as the % of the known added amount of analyte recovered from a spiked test item Working range - The range of an analytical method is the interval between the upper and lower levels, of an analyte, that have been demonstrated to be determined with a suitable level of precision, accuracy and linearity, using the method as written. The working range is normally expressed in the same units as the test results obtained by the analytical method. (Huber: 8.3) 3.15 Uncertainty of Measurement (Measurement Uncertainty) - Parameter associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (Eurachem: 8.1) SANAS Page 5 of 9

6 4. Introduction 4.1 Method validation is the process of establishing the performance characteristics, limitations and acceptance criteria of a method and the identification of the influences which may change these characteristics and to what extent. It is also the process of verifying that a method is fit for purpose. (Eurachem: 8.1) 4.2 Verification refers to a process that provides evidence that the laboratory can achieve the performance characteristics obtained during method validation and demonstrating that the method is suitable for the intended use. (Eurachem: 8.1) 4.3 It is preferable to use this guideline, but if an individual laboratory uses a different approach, it is their responsibility to prove the validity of their approach, with the necessary literature references and/or historical data. 4.4 Validation is always a balance between costs, risks and technical possibilities and the decision should be based on business, regulatory and accreditation requirements. 4.5 For clarification on the extent of method validation or verification, see Table 1. This table has been adapted from PALCAN Guidance for the Validation of Test Methods. (PALCAN: 8.6) Table 1: Extent of method validation:(palcan: 8.6) Test method description Standard published method. Standard published method plus additional documentation for optional steps. In-house developed method. Method published in scientific literature with or without limited performance data. Test method description Methods published in scientific literature with performance data. Changes in the implementation to previously validated methods. Standard published method applied to different matrices, different concentration ranges, analytes or a standard published method used for a similar purpose but different conditions. Archived standard published or previously validated method that is re-instated. Ad hoc or special analyses.(not included in previous validations) Commercial Test Kits collaboratively tested, third party evaluation Commercial Test Kits no performance data available, incomplete or not applicable. Validation or verification requirements Confirmation of published performance characteristics by verification (See paragraph 2.2) in accordance with the requirements of ISO/IEC 17025:2005 section Full validation if changes were made. Full validation. Full validation. Validation or verification requirements Confirmation of published performance characteristics by verification but more likely full validation required. Changes i.e. equipment, reagents, laboratory environment, concentration, matrices and different conditions. The extent of validation will vary to demonstrate that the change does not have a significant impact on performance characteristics. Validation is required and the extent will vary, e.g. having similar properties to those of representative matrices and analytes. Confirmation of previous performance characteristics by verification. Validation is required and the extent will vary, e.g. having similar properties to those of representative matrices and analytes. Confirmation of published performance characteristics by verification but validation may be required if any changes are made or the matrices differ. Full validation. SANAS Page 6 of 9

7 5. Validation Plan (Huber: 8.3) The scope of the method, its validation parameters and acceptance criteria should be defined early in the process. These could include, but may not be limited to the following questions: i) What analytes should be detected? ii) iii) iv) What are the sample matrices? What is the expected concentration levels/measurement range? Are there interfering substances expected, and, if so, should they be detected and quantified? v) Are there any specific legislative or regulatory requirements or what is the purpose of the measurement? vi) vii) How robust should the method be? Should information be qualitative or quantitative? viii) To what extent may the accommodation and environmental conditions influence the method? ix) Which type of equipment should be used? Is the method for one specific instrument, or could it be used by all instruments based on the same principle? x) Is it a standard method, non -standard method or an in house developed method and will the method be used in a specific laboratory or around the globe? xi) The method s performance characteristics/parameters should be based on the intended use of the method. The following characteristics may be included: - Accuracy - Bias (systematic error) - Limit of detection - Limit of quantitation - Linearity - Precision (Random error) - Repeatability - Reproducibility - Robustness - Ruggedness - Selectivity or Specificity - Sensitivity - Recovery - Working range - Uncertainty of measurement SANAS Page 7 of 9

8 6. Implementation, Evaluation, Reporting and Documentation The laboratory should ensure that: i) Sufficient replicates (a minimum of at least 8) of data are used to ensure statistical validity ii) iii) iv) Appropriate statistical tools (formulas and tests e.g ANOVA, T-test, standard deviation, mean etc) are applied to data obtained A rounding off policy is used to ensure that insignificant figures are dropped A statement on the fitness for intended use, based on the performance of the method and that the acceptance criteria are met, is available v) Documented evidence of obtained data and relevant contributing information (e.g calculations, information about equipment, reagents, calibrations, etc.) are kept as evidence and are readily available vi) There is reference to the validation procedure or plan used to generate the test method performance criteria (e.g relevant SOP, validation plan, references) vii) The final validation report was approved by an experienced analyst 7. Revalidation The laboratory is expected to continually prove that the validation is still current through the quality control procedures that include the method s performance characteristics/parameters. Part or full revalidation may be considered when: i) new instrument is introduced, ii) new samples with new compounds or new matrices are introduced (Huber: 8.3), iii) a new location with different environmental conditions is used (Huber: 8.3), iv) new chemicals and/or reference standards are used (Huber: 8.3), v) modifications are implemented due to analytical problems (Huber: 8.3), vi) vii) a review of quality control indicates an established method is changing with time, scheduled as per laboratory procedures, viii) in the case of the method performance criteria falling outside the acceptance criteria (Hube 8.3) Note : In the case where a new analyst is appointed to perform analysis, the laboratory is expected to ensure that the analyst is competent and meets the method s/relevant procedure s performance criteria. SANAS Page 8 of 9

9 8. Guidelines for Assessors (PALCAN: 8.6) The following questions may guide assessors during assessments and assist the laboratory in their preparation for method validation: i) How are test methods selected by the laboratory? ii) iii) iv) Is the laboratory knowledgeable about validation and do they have access to relevant documents? Does the laboratory have procedures for assuring the quality of test results generated by test methods used for routine/ad hoc/ non-routine testing? Does the laboratory have procedures for method validation? v) Who is assigned responsibility for validations? Is the staff trained in conducting validations and evaluating of raw validation data? vi) vii) viii) ix) Is there a separation in the technical records between method development and validation? Is the validation documentation complete, including the raw data? Is there evidence that the method has been successfully transferred to routine use? Is there a process to review performance data generated for methods in routine use to demonstrate to client s ongoing fitness for purpose? x) Is the method declared fit for purpose according to the laboratory s acceptance criteria? xi) What is the basis of choosing the laboratory s acceptance criteria? SANAS Page 9 of 9