Introduction to method validation

1 Introduction tomethod validationWhat is method validation ? method validation provides documented objectiveevidence that a method measures what it is intendedto measure, with acceptable performance parameterssuch as bias and precision. It is a continuation of methoddevelopment and aims to assess and, if necessary,optimise method performance in a way that meets yourcustomer s needs in a cost effective of validation1 validation has three parts and when applied tomethod validation , these translate as:1. The specific intended use is the analyticalrequirement which is set by the problem that theanalysis is intended to The objective evidence is usually in the form ofdata from planned experiments, from which theappropriate method performance parameters The confirmation is taken as a satisfactorycomparison of the method performanceparameters with what is required, evidence that the method is fit for is method validationnecessary?

2 method validation is an essential part of goodmeasurement practice, because valid data can onlybe produced when the strengths and weaknesses of amethod are understood. For the same reasonsmethod validation is an important requirement oflaboratory accreditation to ISO/IEC 17025:20051. When do you need to validatemethods? validation usually begins during the methoddevelopment stage, when some performanceparameters are evaluated approximately to determinewhether the method s capabilities are in line with thelevels required.

3 If a previously validated method hasnot been used for a period of time, its performanceshould be checked (verified) before it is reinstated. Ifthe scope of the method is altered, the method isto be applied to different sample types or analytelevels than it was originally validated for, theperformance must be validated for the new type ofsample. It is important to remember that you mustverify the performance of all test methods before theyare used for the analysis of customer samples,including published and standard methods which havebeen validated by do you validate methods ?

4 method validation should always be a planned first stage is to examine the problem. Look at thereasons behind carrying out the analysis and find outwhat it is that the customer hopes to establish fromhaving the work carried out. It should then be possibleto decide which method performance parameters arerelevant to the work and the target values that arerequired for each parameter. A set of experiments canthen be designed which can be used to evaluate theperformance of the chosen planning a method validation study it is alsoimportant to consider how the experimental data willbe analysed and the statistical tests that will be usedto assess fitness for validation plan should comprise details of thematerial that is going to be analysed to assess eachof the performance parameters.

5 The number ofreplicate measurements required and the statisticalanalysis that will be carried out to evaluate the parameters may be examined in one set ofexperiments in which case the order in which thingsare done can be the plan is formalised, experiments can becarried out to produce data to allow the methodperformance parameters to be evaluated. Theresulting data are compared with the target values todetermine if the method is fit for do you decide fitness forpurpose ?Once the method performance data have beengenerated and collated, an assessment can be madeabout whether the required performance target valueshave been met.

6 If they have been achieved then themethod can be declared fit for purpose andconsidered validated. If the target values are notachieved further development of the method will benecessary, followed by reassessment against thetarget tomethod validation Confirmation, by the examination and theprovision of objective evidence, that theparticular requirements for a specific intendeduse are fulfilled. 11 ISO/IEC 17025:2005. General requirements for the competence of testing and calibration laboratoriesPrecisionSpecificity/selecti vityBiasRuggednessLinearity/working rangeLimit of detectionLimit of quantitationType of analysisQualitativeMajor component Trace analysisPhysical properties The validation processMethod validation builds on the information obtained during method development.

7 The process of validation issummarised in Figure Central to the process is the purposeof the exercise. You need to be clear what the analytical method is intended to achieve. It is useful to consider whether the method evaluation is intended to demonstrate performance against a requirement ( validation ) or performance up to a standard already demonstrated (verification). What performance parameters are critical? The end use should help to define the performance requirements in terms of bias, precision, ruggedness etc.

8 What values should they have? It should be possible to establish some guideline figures for performance. These form the initial performance specification. How should the performance be measured? How much experimentation is required? Once you have the specification it should be possible to plan a set of tests to establish whether the method performance is adequate. The number of tests required can be estimated statistically or by following published best practice or sectoral guidelines. How should the data be interpreted?

9 This could be a simple comparison of performance data with the performance specifications, aided by statistical testing. In some cases the data are reviewed by a third planInterpretationPerformance parametersThe key performance parameters that require attention during validation vary from one analytical requirement to anotherand from method to method , but some commonly important parameters are listed in the table 1: The validation processParameterDifferent method performance parameters will beimportant in different situations.

10 For example, accuracy(precision and bias) will be important for determiningabsolute values of properties or analyte trace work, limits of detection and of quantitation areimportant but these parameters are less important if theanalyte is present at higher concentrations. Whenplanning calibration strategies it is important to know therange over which the response is linear. Ruggednessstudies will indicate which parameters need to becontrolled in order to preserve performance. The amountof validation required will also depend on the source ofthe test method and the extent of any previous validationstudies.