The importance of valid analytical measurements

Transcription

1 The importance of valid analytical measurements

2 The importance of valid analytical measurements Why we need reliable measurements Analytical measurements made in laboratories are always required to fulfil a specific purpose. The laboratory s customers (i.e. the end users of the data) will use the results provided to help answer a particular question and will ultimately make decisions based on the data. If the results provided are not fit for purpose, then performing the analysis is a waste of time and money, and may result in additional costs, or even harm to individuals, companies or the environment. There are always costs associated with unreliable measurements. If measurements have to be repeated, this will result in a direct cost to the laboratory. However, there may also be other costs if unreliable data cause incorrect decisions to be made. For example, a company will incur significant costs if a substandard product is released onto the market as a result of unreliable measurements. Erroneous results can lead to loss of customer confidence. Why we need VAM The DTI s Valid Analytical Measurement (VAM) programme aims to: Improve the reliability of analytical measurements made in the UK; Facilitate mutual recognition of analytical data across international boundaries; Develop a robust and transparent infrastructure aimed at achieving international comparability and traceability of chemical measurements. A set of six principles of good analytical practice was developed as part of the VAM programme. Adopting the principles in your laboratory will not only enable you to reduce costs and avoid risks, but will also allow you to demonstrate the validity and fitness for purpose of your analytical measurements to your customers. This could also be important for your efforts to generate new business. The aim of the six VAM principles is to provide a framework for laboratories to deliver reliable measurements first time every time. If the results of analysis are to be useful, they must be both reliable and credible. At every stage in the analytical process, care must be applied to ensure that no actions are taken that might compromise the intended end use of the results. There must be guidance available which combines the features of both an effective quality management system and good measurement science. This is what VAM provides. The emphasis with VAM is on fitness for purpose. As customers requirements change, the criteria for fitness for purpose will also change. By adopting the VAM principles you will be in a better position to respond to those changing needs. The VAM approach is one of continuous diagnosis and improvement with the goal that your performance will improve with time. VAM Principle 1 Analytical measurements should be made to satisfy an agreed requirement. VAM Principle 2 Analytical measurements should be made using methods and equipment which have been tested to ensure they are fit for purpose. VAM Principle 3 Staff making analytical measurements should be both qualified and competent to undertake the task. VAM Principle 4 There should be a regular independent assessment of the technical performance of a laboratory. VAM Principle 5 Analytical measurements made in one location should be consistent with those elsewhere. VAM Principle 6 Organisations making analytical measurements should have well defined quality control and quality assurance procedures. The full benefits are obtained when all six principles are implemented together. All of the principles need to be addressed by every laboratory, to a degree which is appropriate to each individual organisation. The VAM principles are relevant to the work of laboratories of all sizes and across the full range of activities, from research to quality control. Each of the VAM principles is discussed in detail in the following pages. These sections will help explain why you should implement the VAM principles, how to implement them and where VAM can help you. 1

3 Further information on all the resources mentioned can be obtained from the VAM website, A number of the resources can be downloaded free of charge. The website also provides further details about the VAM programme plus up to date information on current publications, new resources and VAM events. Principle 1 Analytical measurements should be made to satisfy an agreed requirement. The reason for performing any analysis is to solve a defined problem. For example, a foodstuff may be analysed to verify that the nutritional labelling is correct or samples of apples may be tested to ensure that they comply with current legislative limits for pesticide residues. To enable you to deliver results that are fit for purpose you need to have a clear understanding of the question the customer is trying to answer and the end use to which the data will be put. For example, the customer may request the level of lead in a sample of paint to be determined. In some cases it may be appropriate to measure the total concentration of lead in the sample. However, if the sample of paint is from a toy, and the testing is required to demonstrate compliance with toy safety regulations, then it is the amount of lead extracted into a stomach acid simulant under specific conditions that is relevant. If the wrong determination is carried out, the results will be of little use to the customer. A clear understanding of the customer s problems and the measurement objective is necessary to deliver results in the most cost-effective manner consistent with fitness for purpose. Discuss the objective of the measurement with the customer and make sure you have a clear understanding of their requirements. Chose an appropriate analytical method that covers the customer s requirements. Time, cost and quality of the results, i.e. acceptable measurement uncertainty, should all be considered. The Fitness for Purpose of Analytical Methods, 1 st edition, Eurachem (1998) (ISBN: ) In-House Method Validation A Guide for Chemical Laboratories, LGC (2003) (ISBN X) Quality in the Analytical Chemistry Laboratory, 2 nd edition, Wiley (2007) Principle 2 Analytical measurements should be made using methods and equipment which have been tested to ensure they are fit for purpose. Knowledge of method performance parameters such as, precision, bias and measurement uncertainty is required to determine if a test method is capable of producing results that will meet the customer s requirements. For example, the analysis of precious metals will require results with a smaller uncertainty than those produced by screening methods used to look at trace levels of pesticides in foodstuffs. If the performance of test methods and equipment are not assessed prior to the analysis of customer samples, then there is no evidence to demonstrate the validity of the data produced. If the method s performance is not adequate, then the application of the method to customer samples is a waste of time. A test method should be validated for the analysis of particular analytes in a specified concentration range and for specified sample types. If you wish to apply the method to a different sample type or analyte concentration, you will need to verify that the method s performance is still acceptable for the new sample type(s). The performance of your method and equipment is assessed by validation or verification. Validation demonstrates the performance of the method or equipment against a requirement whereas verification demonstrates performance up to a standard already established. Ensure validated methods of analysis are used, this will allow you to demonstrate that the method performance is adequate. Verify the performance of all test methods (including published standard methods) prior to the analysis of customer samples. Put review procedures in place to deal with nonroutine analysis. Ensure that the equipment used operates according to a specification appropriate to the requirements of the method. 2

4 Quantifying Uncertainty in Analytical Measurement, 2 nd edition, Eurachem/CITAC (2000) (ISBN ) available to download at The Fitness for Purpose of Analytical Methods, 1 st edition, Eurachem (1998) (ISBN ) In-House Method Validation A Guide for Chemical Laboratories, LGC (2003) (ISBN X) mval software for method validation, LGC (2003) MV advisor web tool available at P. Bedson and M. Sargent, The Development and Application of Guidance on Equipment Qualification of Analytical Instruments, J. Accred. Qual. Assur. (1996) 1: available to download at For more information about method validation please refer to the leaflet Introduction to method validation in this series. Principle 3 Staff making analytical measurements should be both qualified and competent to undertake the task. Analysts need an appropriate level of knowledge to enable them to understand the methods used. Analysts who are trained and competent are more likely to understand the underlying principles of the methods and be able to identify when problems have arisen, put them right and therefore achieve reliable results. Analysis is a practical activity. Staff must therefore be assessed on their training and competence in carrying out key laboratory operations and applying individual test methods. Ensure appropriate training programmes are devised and implemented for all tasks undertaken and test analysts competence regularly. Use training records that include the assessment of knowledge and skills gained on courses. Practical Laboratory Skills Training Guides (Five booklets plus Practical Laboratory Skills CD-ROM), Royal Society of Chemistry (2003) (ISBN ) VAMSTAT II (A computer-aided learning package for training in statistics for the analytical chemist), LGC (2000) Principle 4 There should be a regular independent assessment of the technical performance of a laboratory. Obtaining an external benchmark of laboratory performance via participation in proficiency testing (PT) schemes provides many benefits. It gives you feedback on your laboratory s technical performance compared with other laboratories making similar measurements, as well as information on the performance of individual staff members. It can help you to improve quality and to make informed choices about methods of analysis and equipment used. Regular independent assessments can be used to demonstrate to customers your commitment to, and achievement of, quality. Proficiency testing provides the infrastructure for a laboratory to monitor and improve the quality of routine analytical measurements. Participate in appropriate proficiency testing schemes or other inter-laboratory comparisons. Have procedures in place for evaluating the results from proficiency tests and for addressing any issues that arise. Customers may be able to provide suitable assessment samples to run along with test samples. This is useful where no proficiency testing scheme exists. Proficiency Testing in Analytical Chemistry, Royal Society of Chemistry (1997) (ISSN ) Ensure personal achievements in training programmes are recorded. 3

5 Principle 5 Analytical measurements made in one location should be consistent with those elsewhere. Disagreements between companies or other organisations over analytical measurements wastes time and money. For example when goods are being exported, test results supplied by the exporting country should be trusted and accepted by the importing country, to reduce the need for retesting. The Water Framework Directive sets requirements for monitoring water quality in rivers that cross country boundaries. For effective monitoring, the results produced in different countries need to be comparable. Frequently, measurements are made for long term monitoring purposes, for example assessing trends in the nutrients in foods. In this case if there are inconsistencies in the measurement results, apparent changes in nutrient levels may be misinterpreted as significant and real effects. The results from all chemical measurements depend upon, and are ultimately traceable to, the values of measurement standards of various types. To achieve comparable results from different locations, use validated test methods and establish the metrological traceability for all measurement results. Ensure the traceability of your results by checking and calibrating the entire method, including all instrumentation and equipment, using appropriate, traceable reference standards, all having a stated uncertainty. Use certified reference materials and reference standards to assess the method s performance at the validation stage. This helps to ensure results are traceable and comparable and therefore reduces disputes. Understand the factors that contribute to uncertainty in measurement results and estimate the overall uncertainty in the results. Knowledge of the measurement uncertainty allows a more meaningful interpretation of results to be made, again reducing the risk of disputes. Traceability in Chemical Measurement: A Guide to Achieving Comparable Results in Chemical Measurement, Eurachem/CITAC (ECTRACE: 2003) available to download at Meeting the Traceability Requirements of ISO 17025: An Analyst s Guide, 3 rd edition, LGC (2005) (ISBN ) available to download at Applications of Reference Materials in Analytical Chemistry, Royal Society of Chemistry (2001) (ISBN ) For more information about traceability please refer to the leaflet Traceability in chemical measurement in this series. Principle 6 Organisations making analytical measurements should have well defined quality control and quality assurance procedures. Procedures are needed to ensure that VAM principles one to five are met and implemented. Having a well defined quality management system will allow you to demonstrate the quality of your work. Quality control procedures are necessary to show that measurement processes are currently fit for purpose. Quality management systems need to respond to changing requirements which leads to continued improvement. Work to a recognised standard such as ISO/IEC or GLP: and put in place quality control procedures to monitor the day to day performance of methods. These include the analysis of known samples, the analysis of reagent and sample blanks and the duplicate analysis of test samples. This will allow you to identify and correct problems before the results reach your customers. Quality Assurance for Research and Development and Non-Routine Analysis, Eurachem (1998) (ISBN ) Quantifying Uncertainty in Analytical Measurement, 2 nd edition, Eurachem/CITAC (2000) (ISBN ) available to download at Quality in the Analytical Chemistry Laboratory, 2 nd edition, Wiley (2007) 1 2 ISO/IEC 17025:2005. General requirements for the competence of testing and calibration laboratories GLP:1999. The Good Laboratory Practice Regulations

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