how to validate analytical methods

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How to validate analytical methodsRoger Wood*Food Contaminants Division, Joint Food Safety and Standards Group, Ministry of Agriculture,Fisheries and Food, c /o Institute of Food Research, Norwich Research Park, Colney,Norwich NR4 7UQ, UK

The requirement for laboratories to use a `fullyvalidated' method of analysis is now acceptedor required in many sectors of analysis. Fullyvalidated means that a method must havebeen assessed in a collaborative trial. The sig-ni¢cance of these requirements is describedbecause analysts will increasingly berequired to justify their choice of method inthe light of them. In addition, the requirementsand procedures that may be used to obtainmethods that have been validated `in-house',without full validation through collaborativetrial, are also outlined in the article, thesepointing the way to international acceptanceof such methods in future as the cost of carry-ing out full validation of methods throughcollaborative trials becomes prohibi-tory. z1999 Published by Elsevier ScienceB.V. All rights reserved.

Keywords: Analytical method; Validation; Collaborative trial;Study; Legislation

1. Introduction

The selection and development of methods of anal-ysis has traditionally been a subject of importance tolaboratories working in analytical laboratories, oftento the extent that the practical application of themethod is neglected. Possibly, this greater emphasisis because most organisations, be they governmentalor one of the International Standardising Organisa-tions working in some areas, develop methods of anal-ysis, incorporate them into legislation or InternationalStandards but then do not have any mechanism toassess how well such methods are being applied. How-ever, this approach is becoming superseded with theneed to demonstrate that the application of the method

is also being successfully achieved. In addition ana-lysts will be allowed a greater freedom of choice ofanalytical method provided the method chosen meetscertain pre-de¢ned criteria. This so-called criteriaapproach or performance-based approach towardsmethods of analysis is being progressively adoptedby legislative authorities. Thus the emphasis on themethods of analysis, particularly for foodstuffsareas, is now changing with the formal legislativerequirement for and introduction of accreditation,pro¢ciency testing and de¢ned internal quality controlprocedures into the laboratory. Nevertheless it isessential that the quality of the method of analysis isfully recognised and appreciated, this particularly withthe introduction of the criteria approach as analystswill increasing have to justify their choice of method.

Notwithstanding other quality assurance require-ments, laboratories must ensure the quality of alltheir analytical methods in use; they must be validatedand veri¢ed. The various means of ensuring the qual-ity of methods vary from one analytical discipline tothe other and the objective of the analysis in£uencesthe extent of the quality assurance work. The require-ments on methods used in process control are, forexample, generally less demanding than the require-ments on methods for end product control and of¢cialfood control.

The necessity for laboratories to use a `fully vali-dated' method of analysis is now universally acceptedor required within many sectors of analysis. A descrip-tion of these requirements is therefore given below asanalysts will increasingly be required to justify theirchoice of method in the light of these `fully validated'requirements. The meaning of `fully validated' withinthe food sector is illustrated by the requirements of thevarious international organisations which develop oradopt standard methods of Analysis; these aredescribed in the ¢rst part of this paper.

Most method validation guides start with discus-sions on how criteria such as speci¢city, accuracyand precision of the method shall be established. Theanalytical problem, requirements of the customers andchoices of analytical principles are seldom mentioned

0165-9936/99/$ ^ see front matter ß 1999 Published by Elsevier Science B.V. All rights reserved.PII: S 0 1 6 5 - 9 9 3 6 ( 9 9 ) 0 0 1 5 0 - 8

*Corresponding author. Tel.: +44 (0) 1603-255000;Fax: +44 (0) 1603-507723.E-mail: [email protected]

624 trends in analytical chemistry, vol. 18, nos. 9+10, 1999

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in this context. The introduction of a `criteriaapproach' can also be seen as a way of introducing a`customer approach' into method validation discus-sion. Quality can be de¢ned as `ful¢lling the customerrequirement', something that is possible only when themethod to be used is suitable for solving the analyticalproblem.

The ¢rst step in a `full validation procedure' there-fore should be to identify and document `customerrequirements' and the analytical problem, what is ana-lytically and economically possible and other speci¢crequirements on sampling, laboratory environment,external environment, etc. A `validation plan' shouldbe written that indicates the method criteria neededand addresses questions such as:

à when is the method going to be used (e.g. of¢cialfood control and in-house process control methodsmay have to ful¢l different criteria on e.g. precisionand accuracy),

à what type of answer is required ^ qualitative orquantitative, and

à in what state is the analyte, i.e. whether is it bound,free, etc.

This article describes the requirements for methodsof analysis, and in particular the extent of the valida-tion required and the considerations to be made in theirselection. It is divided into three parts, these being:

à Introduction and the acceptability of methods ofanalysis, types of validation, the requirements ofof¢cial organisations and the criteria approach formethods of analysis.

à The requirements for and procedures to obtainmethods that have been fully validated throughcollaborative trials.

à The requirements for and procedures to obtainmethods that have been validated `in-house'.

2. Introduction and the acceptability ofmethods of analysis, types of validationand the criteria approach for methods ofanalysis

Analytical methods must be selected on the basis ofcustomer needs. In many cases this is possible only ifthe laboratory assists the customer to select themethod, since they often lack speci¢c analytical com-petence. Prerequisite for a successful selection is thatthe purpose of the analysis or examination, togetherwith other speci¢c needs, is well documented in ananalytical order / request or in a project or study plan.

Laboratories carrying out analytical work forof¢cial control do not always have the freedom toselect the method. In particular microbiological meth-ods are often laid down in the legislation, e.g. both EUand national legislation frequently specify whichreference methods are to be used in cases of dispute.

In some cases laboratories use internally ( in-house )developed methods or signi¢cantly modify standardmethods. Such methods must be validated at the rele-vant concentration ranges, before being taken into rou-tine use.

If the method of choice is an established standardreference method from, for example, the AOACINTERNATIONAL, the laboratory usually onlyneeds to verify that it can achieve the performancecharacteristics given in the method, especially true-ness and precision, and demonstrate that the methodis suitable for the intended use ( see Table 1). Theextent and nature of such veri¢cation work depend

Table 1

Existing validation Laboratory requirement

Fully validated method (has been studied ina collaborative trial )

Veri¢cation that the laboratory is capable of achieving the performance character-istics of the method (or is able to ful¢l the requirements of the analytical task)

Fully validated method, but new matrix ornew instruments used

Veri¢cation of trueness and precision; possibly also the detection limit

Well-established, but not collaborativelystudied method

Veri¢cation, supplemented with limited validation (e.g. with regard to reproducibility )

Method published in the scienti¢c literature;characteristics given

Veri¢cation, supplemented with limited validation (e.g. with regard to repeatabilityand reproducibility )

Method published in the scienti¢c literature;no characteristics given

Full validation and veri¢cation

Method developed in-house Full validation and veri¢cation

trends in analytical chemistry, vol. 18, nos. 9+10, 1999 625

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on the needs of the customer. If, for example, themethod can give 1% precision whilst only 5% isneeded, it is usually suf¢cient if the laboratory isable to demonstrate that 5% precision is achieved.

It has to be appreciated that far from all the methodswhich have been adopted and published by the interna-tional standardising organisations have been validatedin full method-performance interlaboratory (collabo-rative ) trials. Further information on validation andveri¢cation of analytical methods is given in Sections3 and 4 of this paper.

2.1. The introduction of a new or unfamiliarmethod into the laboratory

2.1.1. Responsibility for carrying out validationand veri¢cation

When a laboratory intends to use a method withwhich it is unfamiliar it is the responsibility of thelaboratory to verify that it is competent to use themethod. Usually national or international organisa-tions, such AOAC INTERNATIONAL, InternationalOrganisation for Standardization ( ISO) etc., haveundertaken the interlaboratory validation of themethod in a method performance (collaborative)trial. The extent of laboratory internal validation andveri¢cation depends on the context in which themethod is to be used. Some suggestions as to the extentof validation and veri¢cation measures are given inTable 1.

2.1.2. Competency requirementsThe introduction of new analytical methods

requires that both the parties developing and validat-ing them, and the laboratory that will subsequentlyverify its ability to use them routinely are suf¢cientlycompetent, i.e. are suf¢ciently knowledgeable, expe-rienced and pro¢cient. When new analytical tech-niques based on, for example, immunological orDNA properties are considered, the laboratory mayhave to employ new staff with speci¢c competence.

It is not unusual for new rapid test kits to be mar-keted with the comment that they are `̀ so simple thatanyone can use them''. Often this is not correct and it isnecessary for the laboratory to acquire new knowledgeor otherwise widen its competence before starting touse the kit. Manufacturers of rapid analysis kits some-times make minor changes both in the documentationand in the composition of the kit; it is therefore neces-sary for the user to be knowledgeable and observantbut also that any instructions accompanying the kitsetc. are carefully read. Knowledge of components

included and inter-batch variation may be of criticalimportance when, for example, polyclonal antibodiesare used in ELISA analyses, or Tris buffers are used inPCR analyses.

2.1.3. Evaluation of published validation andveri¢cation data

Validation results, i.e. the performance character-istics of analytical methods, are often given as repeat-ability and reproducibility data, normally as standarddeviations or relative standard deviations.

The value of the published data varies depending onthe extent of the validation or veri¢cation. In somecases results are based on experiments carried outusing synthetic aqueous standard solutions. Theresults in such cases are naturally not applicable tothe same analyte present in a complex matrix. Inother cases method studies have been appropriatelycarried out in accordance with internationally estab-lished protocols ( see Section 3). In order to give theuser the possibility of evaluating and utilising pub-lished results it must be clearly described how theperformance characteristics were estimated or deter-mined.

Methods published in the scienti¢c literature areoften accompanied by insuf¢cient information on thenature and extent of quality assurance measuresapplied during the validation of the method, such asa description of how important analytical parameters( temperature and pH) were controlled. It is alsoimportant to know whether the originating laboratoryhas participated in pro¢ciency testing schemes or hasused reference materials to support the developmentwork, and indeed whether it had been subjected to anythird party evaluation, e.g. through formal accredita-tion.

The absence of performance characteristics or lackof information on the general competence of the orig-inating laboratory makes it dif¢cult to assess the cred-ibility of incomplete validation data published inmethods.

2.1.4. Using a new or unfamiliar methodBefore taking new or unfamiliar methods into rou-

tine use the appropriate staff must decide if the require-ments of the customer and of the analytical problemare being met. The judgement should be based bothon published validation data and on experimentaldata resulting from the laboratory's own veri¢ca-tion work. Methods should be formally approved inwriting, and their ¢elds of application clearlydescribed.


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The following aspects should be considered:

à the standard operating procedure, and its avail-ability,

à what information the laboratory has on the method:is it based on a standard or reference method, or hasit been developed in-house?,

à whether any deviation in a method as compared tothe `reference method' is fully described and theeffects of the deviation have been investigated,

à whether the method has been veri¢ed, e.g. byanalysing spiked samples of relevant matrices,

à whether the method has been in use in thelaboratory for a time period of a minimum of,say, 3 months during which a number of `real'samples of relevant types have been analysed,

à whether quality control procedures are in place, e.g.analysis of reference or control materials, or controlstrains,

à whether the laboratory participates in pro¢ciencytesting schemes and evaluates, on a continuousbasis, the results,

à whether the measurement uncertainty has beenestimated, and

à if a sensory laboratory, whether it monitors theperformance of individual sensory assessors and ofpanels.

2.2. Requirements of legislation and internationalstandardising agents for methods of analysis

The development of methods of analysis for incor-poration into international standards or into foodstufflegislation was, until comparatively recently, not sys-tematic. As a consequence not all the present standardmethods have been collaboratively validated; even ifcollaboratively validated, the method performancecharacteristics are not always published as part ofthe method thus making it dif¢cult for the analyst toverify his or her capability to use the method in anappropriate way.

In general, it is more common for chemical stand-ard methods to be `fully validated' and suppliedwith information on e.g. precision ( reproducibilityand repeatability ) than is the case for microbiol-ogical methods. One reason why there are few`fully validated' microbiological methods is thatthere are no dedicated guidelines on method validationfor microbiological methods; in practice the chemicalprotocols are adapted by the microbiologicalsector but this is not being carried out in a systematicmanner.

Most international organisations now developtheir own methods in a de¢ned way or stipulateconditions to which their methods should comply. Inthe food sector the most important of these, i.e. theCodex Alimentarius Commission, European Union,the European Committee for Standardisation (CEN)and the AOAC INTERNATIONAL (AOACI) arevery similar. Although these organisations are tar-geted towards the food sector, they may be takenas indicative of the direction that all sectors are mov-ing.

The essential requirement of all these organisationsis that the method has been subjected to a collaborativetrial before it is adopted or recommended by thatorganisation. There are other possibilities for thestandardisation of a method, i.e. through the resultsof pro¢ciency testing schemes or through an in-house validation, but the ¢rst and `easiest' procedurefor a laboratory seeking a method for any particularanalyte / matrix combination is to use a method pub-lished by one of the international standardising organ-isations.

The requirements of the four main non-commodityspeci¢c methods standardising organisations in thefood sector are very similar so only the EU require-ments are described below.

2.2.1. Requirements of the European UnionThe European Union is attempting to harmonise

sampling and analysis procedures to meet the currentdemands of the national and inter-national enforce-ment agencies and the likely increased problemsthat the open market will bring. To aid this the EUissued a Directive on Sampling and Methods of Anal-ysis [ 1 ]. The Directive contains a technical annex, inwhich the need to carry out a collaborative trial on amethod before it can be adopted by the Community isemphasised.

The criteria to which Community methods of anal-ysis for foodstuffs should now conform are as strin-gent as those recommended by any InternationalOrganisation following adoption of the Directive.The requirements are given in the Annex to the Direc-tive. They are:

1. Methods of analysis which are to be consideredfor adoption under the provisions of the Directiveshall be examined with respect to the followingcriteria:

1.1. speci¢city1.2. accuracy


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1.3. precision; repeatability intra-laboratory (withinlaboratory ), reproducibility inter-laboratory(within laboratory and between laboratories )

1.4. limit of detection1.5. sensitivity1.6. practicability and applicability under normal lab-

oratory conditions1.7. other criteria which may be selected as required.

2. The precision values referred to in 1.3 shall beobtained from a collaborative trial which hasbeen conducted in accordance with an interna-tionally recognised protocol on collaborative tri-als (e.g. International Organisation for Standard-isation Precision of Test Methods ( ISO 5725/1981) [ 2 ]). The repeatability and reproducibilityvalues shall be expressed in an internationallyrecognised form (e.g. the 95% con¢dence inter-vals as de¢ned by ISO 5725/1981). The resultsfrom the collaborative trial shall be published orbe freely available. [Note: this reference hassince been updated and only the latest referenceis now cited.]

3. Methods of analysis which are applicable uni-formly to various groups of commodities shouldbe given preference over methods which apply toindividual commodities.

4. Methods of analysis adopted under this Directiveshould be edited in the standard layout for meth-ods of analysis recommended by the Interna-tional Organisation for Standardisation.

2.2.2. Requirements of of¢cial bodies ^ the validanalytical method

Consideration of the above requirements means thatall legislative methods from the European Union mustbe fully validated, i.e. have been subjected to a collab-orative trial conforming to an internationally recog-nised protocol. In the food sector this is also followedby the Codex Alimentarius Commission as well asmethods of analysis stemming from the main ISOs.Indeed, these requirements are now adopted by mostother international bodies. Thus it is essential that lab-oratories use methods which comply to the require-ments in order to be able to ensure acceptance oftheir analytical methodology by their customers.

The concept of the valid analytical method is suchthat the accuracy and precision (now trueness ) of themethod are determined.

2.3. Future requirements for methods of analysis^ criteria of methods of analysis

Notwithstanding the above there is now an increas-ing tendency for the laboratory to be allowed freedomof choice of the analytical method. This is because it isnow recognised that for a laboratory to report satisfac-tory (and acceptable ) analytical results it must under-take a number of measures, only one of which is tochoose and use an appropriate or prescribed method ofanalysis. This is best illustrated by consideration ofactivities in:

1. GATT, where the agreement on the Applicationof Sanitary and Phytosanitary Measures recom-mends mutual recognition between govern-ments. For the Codex Alimentarius Commission,this means that the concept of equivalence shouldbe adopted,

2. the Codex Alimentarius Commission, which hasendorsed the Codex Alimentarius Commissionthe IUPAC /ISO /AOAC Harmonised Protocolfor the Pro¢ciency Testing of (Chemical ) Ana-lytical Laboratories [ 3 ], and the CCMAS whichis recommending for endorsement by the CodexAlimentarius Commission the IUPAC /ISO /AOAC Harmonised Guidelines for InternalQuality Control in Analytical Chemistry Labo-ratories [ 4 ] and which, at its Twenty-¢rst Ses-sion, recommended laboratory quality standardsfor laboratories involved in import / export cer-ti¢cation work [ 5 ],

3. the EU, where as a result of the adoption of theAdditional Measures Food Control Directive[ 6 ], food control analytical laboratories will berequired to become accredited ( to the Europeanequivalent of ISO Guide 25), participate in pro¢-ciency testing schemes and to use fully validatedmethods whenever such methods are available.Such validation for methods equates to therequirements for methods of analysis outlinedin the Codex Alimentarius Commission's Proce-dural Manual [ 7 ].

As a result of such activities the focus of attention ismoving towards how well the analyst ( laboratory )carries out his analytical procedures and away fromjust ensuring that he is using a prescribed analyticalmethod.


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3. The requirements for and proceduresto obtain methods that have been fullyvalidated through collaborative trials

As seen from the above, all `of¢cial' methodsof analysis are required to include precision data;such data can only be obtained through a collabor-ative trial and hence the stress that is given to collab-oratively tested and validated methods in the foodsector.

3.1. What is a collaborative trial?

A collaborative trial is a procedure whereby theprecision of a method of analysis may be assessedand quanti¢ed. The precision of a method is usuallyexpressed in terms of repeatability and reproducibilityvalues. Accuracy is not the objective. Because of theimportance of collaborative trials they are described ingreater detail below using the Outline and Recommen-dations from the IUPAC /ISO /AOAC HarmonisedProtocols.

3.2. IUPAC / ISO / AOAC INTERNATIONALharmonisation protocol

Recently there has been progress towards a univer-sal acceptance of collaboratively tested methods andcollaborative trial results and methods, no matter bywhom these trials are organised. This has been aidedby the publication of the IUPAC /ISO /AOACINTERNATIONAL Harmonisation Protocols on Col-laborative Studies [ 8,9 ]. These Protocols were devel-oped under the auspices of the International Union ofPure and Applied Chemists ( IUPAC) aided by repre-sentatives from the major organisations interested inconducting collaborative studies. In particular, fromthe food sector, the AOAC INTERNATIONAL, theInternational Organization for Standardization ( ISO),the International Dairy Federation ( IDF), the Collab-orative International Analytical Council for Pesticides(CIPAC), the Nordic Analytical Committee(NMKL), the Codex Committee on Methods of Anal-ysis and Sampling and the International Of¢ce ofCocoa and Chocolate were involved.

The Protocols give a series of recommendations;they address the topics listed below:

à The components that make up a collaborative trial

à Participants

à Sample type

à Sample homogeneity

à Sample plan ^ number of materials (material^analyte/concentration level/matrix combination)

à Number of replicates

à Split level (single or double)

à Combination blind replicates and split level

à Blind replicates

à Known replicates

à Independent replicate analyses

à The method(s) to be tested

à Pilot trial/pre-trial

à The trial proper

à Statistical analysis

à Valid data

à One-way analyses of variance

à Initial estimation

à Outlier treatment

à Precision parameters

à Final report

3.3. Other procedures for the validation of amethod of analysis

International organisations are now consideringother procedures for the validation of methods of anal-ysis besides a complete collaborative trial. Instruc-tions on the use of results from pro¢ciency testingschemes have been developed by the UK Ministry ofAgriculture, Fisheries and Food [ 10 ] and there is nowa procedure for the validation of test kit methodsdeveloped under the `MicroVal' project.

3.4. Assessment of the acceptability of theprecision characteristics of a method of analysis:calculation of HORRAT values

There is no formal requirement in the EuropeanUnion or in Codex as to the acceptability of the pre-cision characteristics of any particular method. How-ever, the calculated repeatability and reproducibilityvalues can be compared with existing methods and acomparison made. If these are satisfactory then themethod can used as a validated method. If there is nomethod with which to compare the precision parame-ters then theoretical repeatability and reproducibilityvalues can be calculated from the Horwitz equation[ 11]. This is best achieved by the use of HORRATvalues to give a measure of the acceptability of theprecision characteristics of a method.

The HORRAT value is: (RSDR derived from thecollaborative trial )/(RSDR predicted from the Horwitzequation).


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Thus, HoR, the HORRAT value for reproducibility,is the observed RSDR value divided by the RSDR

value calculated from the Horwitz equation at the con-centration of interest.

3.5. Interpretation

If the HORRAT values are 2 or less, then the methodmay be assumed to have satisfactory reproducibilityvalues. Laboratories should ensure that the methodswhich they employ meet this criterion.

3.6. Calculation of the Horwitz value

The Horwitz value is derived from the Horwitzequation, which states that for any method:

RSDR � 2�130:5logC�

and that the value is independent of matrix / analyte.The major values are:

Horwitz has derived the equation after assessing theresults from many (V3000) collaborative trials.Although it represents the average RSDR values andis an approximation of the possible precision that canbe achieved, the data points from àcceptable' collab-orative trials are less than twice the predicted RSDR

values at the concentrations of interest. This idealisedsmoothed curve is found to be independent of thenature of the analyte or of the analytical techniquethat was used to make the measurement. In generalthe values taken from this curve are indicative of theprecision that is achievable and acceptable of an ana-lytical method by different laboratories. Its use pro-vides a satisfactory and simple means of assessingmethod precision acceptability.

This procedure is increasingly being used by organ-isations to assess the acceptability of the precisioncharacteristics of their methods.

4. The requirements for and proceduresto obtain methods that have beenvalidated ìn-house'

It is a requirement that in many sectors that methodsof analysis should, wherever possible, be fully vali-dated, i.e. have been subjected to a collaborative trial.There are, however, many situations where this is notfeasible or such methods are not available, and indeedmany sectors do not take this approach. As a result theneed for laboratories to develop and use their own in-house methods of analysis is well recognised in theanalytical community. Until recently such in-housemethod validation has been undertaken on an ad hocbasis. It has become recognised that such validationshould be carried out on a more formal basis and anumber of organisations have developed proceduresand protocols which meet such needs. The Codex Ali-mentarius Commission has agreed that the topicshould be included in its formal work programme[ 12 ]. In particular, it is recognised within the Codexsystem that there are some sectors of food analysis,e.g. the veterinary residues in food sector, where it isvery unlikely that fully validated methods are, orlikely to become, available.

Validation can be de¢ned as the process of deter-mining the suitability of a measurement system forproviding useful analytical data. The term interlabor-atory comparison ( i.e. collaborative trial ) is oftentaken to be synonymous with method validation inthe food sector. According to ISO / IEC Guide 25,this is but one of a number of ways of validating ana-lytical methods. The others include one or more of thefollowing:

à calibration using references or reference materials;

à comparison of results achieved with other methods;

à systemic assessment of the factors in£uencing theresult; and

à assessment of the uncertainty of the results basedon scienti¢c knowledge and practical experience.

As stated previously ISO, IUPAC and AOACINTERNATIONAL have co-operated to produceagreed protocols or guidelines on the `Design, Con-duct and Interpretation of Method Performance Stud-ies' [ 8,9 ] on the `Pro¢ciency Testing of (Chemical )Analytical Laboratories' [ 3 ] on Ìnternal QualityControl in Analytical Chemistry Laboratories' [ 4 ]and on the use the use of recovery information in ana-lytical measurement [ 13 ]. The working group that

Concentration ratio RSDR

1 (100%) 21031 2.81032 (1%) 41033 5.61034 81035 111036 (ppm) 161037 231038 321039 (ppb) 45


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produced these protocols /guidelines has been man-dated by IUPAC to prepare guidelines on the in-house validation of methods of analysis. These guide-lines will outline minimum recommendations to labo-ratories producing analytical data on procedures thatshould be employed to ensure adequate validation oftheir methods before undertaking further validationinvolving other peer laboratories. The Guidelines areintended to be generally applicable across the analyt-ical community. Appendix A gives an indication of thetopics that will be addressed in the Guidelines.

A draft of the guidelines will be discussed at anInternational Symposium on the Harmonisation ofQuality Assurance Systems in Chemical Laboratory,the proceedings from which will be published by theUK Royal Society of Chemistry.

4.1. Protocols for the in-house validation ofanalytical methods

There are a number of authoritative texts whichhave been developed for the in-house validation ofanalytical methods, and in particular:

A Protocol on the Validation of Chemical Ana-lytical Methods developed by the Nordic Com-mittee on Food Analysis [ 14 ],A generic laboratory guide developed by EUR-ACHEM produced by the UK Laboratory of theGovernment Chemist with the support of the UKDepartment of Trade and Industry Valid Analyt-ical Measurement Initiative [ 15 ],An Interlaboratory Analytical Method Valida-tion Short Course developed by the AOACINTERNATIONAL [ 16 ],A Guide to the Validation of Methods developedby the Dutch Inspectorate for Health Protection[ 17 ], andA guide to Analytical Quality Assurance in Pub-lic Analyst Laboratories prepared by the UKAssociation of Public Analysts [ 18 ].

They will be considered by the IUPAC Group pre-paring its Guidelines.

5. Conclusions

It is now recognised that methods must be validatedbefore use. Ideally methods should be `fully vali-dated', i.e. have been subjected to a collaborativetrial which itself complies with internationally

accepted protocols. However, with the requirementfor laboratories to comply with de¢ned quality stand-ards, and because of the dif¢culty of obtaining suf¢-cient participants to enable collaborative trials to becarried out in every situation ( i.e. for every combina-tion of analyte / matrix ) there is now a requirement foran internationally accepted set of guidelines dealingwith in-house methods to be developed. This is beingaddressed by IUPAC.

Appendix

Contents of IUPAC guidelines on in-house method validation

The contents of the Guidelines will be such that thefollowing will be addressed:

IntroductionDe¢nitions and terminology used in guidelinesConcepts and general principlesThe introduction of a new or unfamiliar methodinto the laboratoryRequirements for individual parameters

à Applicability

à Selectivity

à Calibration

à Accuracy

à Precision

à Range

à Limit of quanti¢cation

à Limit of detection

à Sensitivity

à Ruggedness

à Practicability

ConclusionsRecommendationsReferencesAppendix I: Extract from Report `Validation ofAnalytical Methods for Food Control' preparedby the FAO /IAEA

References

[ 1 ] Council Directive 85 /591/EEC Concerning the Introduc-tion of Community Methods of Sampling and Analysis


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for the Monitoring of Foodstuffs Intended for HumanConsumption, O.J. L372 of 31.12.1985.

[ 2 ] Precision of Test Methods, Geneva, 1994, ISO 5725 (pre-vious editions were issued in 1981 and 1986).

[ 3 ] M. Thompson, R. Wood (Editors ), The InternationalHarmonised Protocol for the Pro¢ciency Testing of(Chemical ) Analytical Laboratories, Pure Appl. Chem.65 (1993) 2123 (also published in J. AOAC Int. 76(1993) 926).

[ 4 ] M. Thompson, R. Wood (Editors ), Guidelines on internalquality control in analytical chemistry laboratories, PureAppl. Chem. 67 (1995) 649.

[ 5 ] Report of the 21st Session of the Codex Committee onMethods of Analysis and Sampling, FAO, Rome, 1997,ALINORM 97/23A.

[ 6 ] Council Directive 93 /99EEC on the Subject of Addi-tional Measures Concerning the Of¢cial Control of Food-stuffs, O.J. L290 of 24.11.1993.

[ 7 ] Procedural Manual of the Codex Alimentarius Commis-sion, 10th Edition, FAO, Rome, 1997.

[ 8 ] W. Horwitz (Editor ), Protocol for the design, conduct andinterpretation of method performance studies, Pure Appl.Chem. 70 (1998) 855.

[ 9 ] W. Horwitz (Editor ), Protocol for the design, conduct andinterpretation of method performance studies, Pure Appl.Chem. 67 (1995) 331.

[ 10 ] MAFF Validated Methods for the Analysis of Foodstuffs:VOA ^ Introduction, General Considerations and Analyt-ical Quality Control, J. Assoc. Publ. Anal. ( in prepara-tion).

[ 11] W. Horwitz, Evaluation of analytical methods used forregulation of foods and drugs, Anal. Chem. 54 (1982)67A.

[ 12 ] Report of the 22nd Session of the Codex AlimentariusCommission, FAO, Rome, 1997, ALINORM 97/37.

[ 13 ] S. Ellison, M. Thompson, P. Willetts, R. Wood (Editors ),Harmonised Guidelines for the Use of Recovery Informa-tion in Analytical Measurement, Pure Appl. Chem. ( inpress ).

[ 14 ] Validation of Chemical Analytical Methods, NMKL Sec-retariat, Helsinki, 1996, NMKL Procedure No. 4.

[ 15 ] Method Validation ^ A Laboratory Guide, EURACHEMSecretariat, Laboratory of the Government Chemist, Ted-dington, 1996.

[ 16 ] An Interlaboratory Analytical Method Validation ShortCourse developed by the AOAC INTERNATIONAL,AOAC INTERNATIONAL, Gaithersburg, MD, 1996.

[ 17 ] Validation of Methods, Inspectorate for Health Protec-tion, Rijswijk, Report 95-001.

[ 18 ] A Protocol for Analytical Quality Assurance in PublicAnalysts' Laboratories, Assoc. Publ. Anal., Shef¢eld,1986.

Step-by-step implementation of a qualitysystem in the laboratoryMaria Joaì o BenolielEmpresa Portuguesa das Aguas Livres S.A., Laboratorio Central da EPAL, Rua do Alviela 12,P-1170-012 Lisboa codex, Portugal

In recent years laboratories have undergonehuge transformations due to the technologi-cal development of inspection and testingequipment; the introduction of computerisedand automated systems; keen competitive-ness between companies / laboratories as aresult of demand within Europe and on theinternational market; and greater consumerawareness of the quality of the products avail-able. Laboratory accreditation, though a vol-untary process, is formal recognition by anaccreditation body of the laboratory's compe-tence to carry out certain tests. This articlepresents those aspects which should betaken into account in the step-by-step imple-mentation of a quality system and also makesreference to the requirements for the opera-

tion of accredited laboratories in accordancewith European Standard EN 45001. z1999Elsevier Science B.V. All rights reserved.

Keywords: Accreditation; Quality assurance system;Validation

1. Introduction

Quality is a daily, on-going challenge contributingto technological and scienti¢c development. Qualityhas also become a factor of competitiveness betweenlaboratories and companies. In recent years there hasbeen growing concern about quality-related aspects asa result of the creation of the internal European marketaccompanied by the trend toward globalisation of the

0165-9936/99/$ ^ see front matter ß 1999 Elsevier Science B.V. All rights reserved.PII: S 0 1 6 5 - 9 9 3 6 ( 9 9 ) 0 0 1 6 8 - 5


how to validate analytical methods

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