Received: 10 September 2001Accepted: 9 November 2001

There is now a general agreementbetween experts that the fundamentalprinciples of metrology based on thekey concept of “traceability” and“uncertainty” are applicable tochemical analyses. However, somefield chemists still need clarificationof the objectives. A working group(WG) composed of one chemicalmetrologist and three pharmaceuticalanalysts, acting under the auspices ofthe French Society for Pharmaceuti-cal Sciences and Technologies havedeveloped a “user friendly” set ofquestions and answers addressingthese matters. Considering that theseexplanations could be useful to fieldchemists, active in other industries

and / or who cannot understandFrench, Prof. Paul De Bièvre, Editorin Chief of ACQUAL recommendedthat the text be published in ACQUAL in English. Readers maylike to refer to the original text [1].Some people would advocate (andbe right) that there is no “chemicalmetrology, but rather an implementa-tion of metrology in chemistry. How-ever, since the term “physical me-trology” is used, we found it usefulto use the term “chemical metrolo-gy”, the main objective being to pre-vent the misunderstanding that me-trology is only a matter for physi-cists.

Accred Qual Assur (2002) 7:42–49DOI 10.1007/s00769-001-0418-y

© Springer-Verlag 2002

REVIEW PAPER

A. MarschalT. AndrieuxP.A. CompagonH. Fabre

Chemical metrology – QUID?

What does “chemical metrology” mean?

According to the international vocabulary of metrology(VIM) [2], metrology is the science of measurement. It isalso specified that metrology encompasses all theoreticalor practical aspects related to measurements, whatevertheir uncertainty and whatever their fields of science ortechnology .

In the chemical field, quantitative chemical analysismay be considered as another name for chemical metrol-ogy. The consequences of this are given in Sect. A.

A more selective approach to metrology is to considerthat its primary vocation is to trace units and standardsof any measurement, analysis or test. Keywords in chem-ical metrology are those of general metrology: measu-rand, uncertainty, traceability.

This aspect of chemical metrology is developed inSect. B, which specifies the motivations, objectives andrequirements which are essential to this exercise.

Since principles are supposed to meet real conditions,we will eventually show and prove, in Sect. C, how theseprinciples are applied to usual cases in the laboratory.

The WG hopes that this document will start a dia-logue that can be pursued and invites readers to askquestions related to their activities.

A. If chemical analysis is a measurement, then what are the consequences?

The consequences are that any body or individual con-cerned with the analysis (expert, designer, operator, user,etc.) needs to think about and find an answer appropriateto the needs on the following points:

– Definition of measurand– Adequacy of the measurand with the need– Traceability to the units and standards

A. MarschalLaboratoire National d’Essais, 1, Rue Gaston Boissier, 75724 Paris Cedex 15, France

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– Organisation of the metrology tasks within the labora-tory and the company

– Estimation of the uncertainty of the analysis.

The last point implies that some statistical models shouldbe specified and applied on the basis of the scientific andtechnical knowledge available on the analysis, and itspractical realisation.

B. What does traceability to units of chemical analysis refer to?

The aim of an analysis is to provide quantitative infor-mation about the sample subjected to the analysis. Thisinformation must have the same meaning to everyone(within uncertainties). This implies that the result shouldbe given in the same unit. To make sure there is world-wide harmony, a complete sequence of comparisons trac-ing1 all the components of the unit used to the SI systemshould be implemented.

In the case of a classical chemical analysis, expressedin mole/l or mole/g or, usually, in mg/l or g/g, it is neces-sary that determination of the test sample and the quanti-fication of the analyte be traced to references from anhigher metrological level. If the analysis is the compo-nent of a more complex determination, such as dissolu-tion kinetics, the main components of the problemshould be separated and this determination should belinked for time, volume, diluent flow rate or any otherrelevant quantity measurement.

Chemists now appreciate this systematic link whenthey carry out physical or physicochemical measure-ments [3].

A.1. Could you specify, by giving examples from chemistry and pharmacy, what is the measurandand what is its adequacy to the need?

The measurand is the particular quantity submitted tomeasurement [2]. It may be for example:

– The amount of ascorbic acid contained in a tablet (mgor mole).

– The aliquot amount of lead in sodium bicarbonate; theresult would then be expressed in mg/kg or mol/kg ofpowder.

To be rigorous, in metrology, the analysis results shouldbe given in moles, but mass units are often used. Most ofthe time, this is not a problem, except when the isotopeof the analyte is not a constant or if colleagues use themole.

This definition of measurand provides the opportunityto check the adequacy between the information receivedand the information expected. For instance, in the case ofthe evaluation of the toxicity due to lead, should wemeasure all the lead present or only tetraethyl lead, orboth separately?

The measurand actually measured depends on themethod and protocol used. Logically, the type of infor-mation needed governs the choice of the measurand, andthe measurand will govern the method and protocol to beused.

A.2. Could you specify, by giving an example fromchemistry and pharmacy, what are traceability and tracing to the SI?

First of all, we need to remind ourselves that the generalmeaning of “traceability” can be summarised as: the ex-istence of a logical continuity of the process, ensuringthat there is no weak nor missing step in the process atany time, thus encumbering or even breaking the effi-ciency of the whole process.

For a chemist, there are three different types of trace-ability:

– Material traceability; the best known of all, which al-lows us to record all the manufacturing history of abatch and, especially, the precise origin of all theproducts used for the manufacturing, as well as the fa-cilities and equipment.

– Documentary traceability, which consists of findingraw data before the analysis report, e.g. the operator’slaboratory notebook, the document specifying themethod (protocol, standards, etc.), tables of constants,calibration certificates, etc.

– Metrological traceability which mostly concerns themetrologist who ensures that the unit stated after themeasured value is universal [4]. This can be ensuredby a logical succession of operations, depending onthe type of analytical method implemented. These op-erations can be, according to the type of method, veri-fication or calibration of the balance or the burette,use of ‘pure’ substances, standard titrated solutionsand reference materials with a determined composi-tion. This point is developed in Sect. B.

From the point of view of the user, all three types oftraceability are important. If one is missing, the othertwo are of no interest or even become useless.

A.3. What does “to organise one’s metrological tasks”mean?

In any field, the ultimate aim of a measurement or analy-sis is to get a quantified result, associated with a certainuncertainty. This implies the definition of a metrologicaltraceability, as specified in the previous paragraph.

1 The word “tracing” is used in the text as the equivalent of thecommonly used French word “raccordement” (cf. VIM 6.10)

Since equipment and method performance, on the onehand, and users’ needs on the other, are not the same inall the cases as far as uncertainty is concerned, all ac-tions should be optimised in order to reach the uncertain-ty required. Adequacy between the method, equipmentand the aim wanted is to be sought. Mouvement Francaispour la Qualité (MFQ) has published a book that canhelp the reader understand the necessity of implementingglobal metrology [5].

A.4. “Uncertainty of analysis” is not commonly used.What does it mean exactly and when is it used?

In order to answer this question it is worth remindingourselves that the aim of an analysis is usually either toestablish the (usage or fiduciary) value of a product, orto follow the specifications (for example, an impuritylevel lower than a threshold specified). Since an analysis(as any measurement) is a man-made operation, it cannot be perfect. Therefore an uncertainty, reflecting thedoubt, must be associated with any result.

According to the standard NF X 07–001 (1994), un-certainty of measurement is the “parameter associatedwith the result of a measurement that characterises thedispersion of the values that could reasonably be attrib-uted to the measurand.”

Notes:

1. The parameter can be, for example, a standard devia-tion ( or a given multiple of it), or a half-width havinga stated level of confidence.

2. Uncertainty of measurement comprises in generalmany components. Some of these can be evaluatedfrom the statistical distribution of the results of seriesof measurements and can be characterised by experi-mental standard deviations. The other components,that can also be characterised by standard deviations,are evaluated from assumed probability distributionsbased on experience or other information.

3. It is understood that the result of the measurement isthe best estimate of the value of the measurand, andthat all components of uncertainty, including thosearising from systematic effects, such as componentsassociated with corrections and reference standards,contribute to the dispersion.

This uncertainty covers both influences of systematic andrandom type effects contributing to the dispersion of thevalues, which can be associated with the measurand.When the value of the product or its conformity with thespecification is significantly modified, when the doubt hasbeen taken into account, then it means that this doubt istoo large and that further knowledge about it is needed. Itis becoming less and less possible to ignore doubt. Doubtmust be dealt with by quantifying it through uncertainty.

The uncertainty obtained can then be compared to theuncertainty looked for, which leads to one of three con-clusions:

– The analysis protocol is well-designed: it is good tohave an objective confirmation.

– The analysis protocol is too coarse: either noncompli-ant batches pass the analysis and are returned asclaims, or more severe tolerances are imposed as aprecaution, but this leads to a downgrade of somebatches.

– The analysis protocol is not justified: the analysis canbe simplified and made cheaper and quicker.

A.4.1. I usually report the standard deviation from a series of assays as the uncertainty. Is it correct to do this?

Uncertainty is by no means standard deviation, but it canbe used to calculate the confidence interval for the aver-age value of a series of results. Nevertheless, the confi-dence interval calculated only takes into account randomerrors, which constitute only one of the components ofuncertainty. Systematic errors must also be taken into ac-count, in as much as corrections have not taken care ofthem (e.g. uncertainty on the correction, forgetting thecorrection).

Taking into account only the repeatability of standarddeviation of a short series of dosages is too optimisticand insufficient. The fact that a comparable series ofdosages made before or after, or by another operator orin another laboratory has significantly different resultsshows that some of the sources of uncertainty have notbeen dealt with as required. Moreover, heterogeneity ofmaterials and sampling is also significant for repeatabili-ty. If the materials are very heterogeneous, the dispersionmust be attributed to the materials rather than to the ana-lytical method. It is then impossible to try to improve themethod. Sampling and homogenisation of the sample arethe points to be addressed [6].

A.4.2. I sometimes use the reproducibility standard deviation, or the reproducibility limit obtained in an interlaboratory comparison as the uncertainty . Is this correct?

This is a more realistic estimation which can sometimesbe acceptable. Before validating this option, the follow-ing points must be discussed:

– Did my laboratory participate in the comparison?– Is my laboratory comparable in terms of equipment

and experience to those which participated in thecomparison?

– Did the participants take special precautions, as isoften the case in an interlaboratory comparison?

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– Is using the same method or part of it (for instanceextraction) for all the laboratories not a risk, creatinga systematic bias for all the participants?If the answer is “yes” to the first two questions and“no” to the last two, then the situation is favourable.Otherwise, the estimation may be too optimistic.Standard NF X 07–021 [7] specifies how to use thisstatistical concept.

A.4.3. What is the recommended method for the estimation of analysis uncertainty?

The method which is now recognised as the best one isdescribed in GUM [8] and has been endorsed by seveninternational organisations whose fields of activities aremetrology, analysis and tests. The reader should refer tothis publication.

Reading the literature[9], in particular that dealingwith analytical chemistry [10], might help us understandthe principles of the method. There are also examplespublished in ACQUAL. The following remarks may helpthe reader understand GUM:

– The basic principle is to identify the defects of themethod followed compared to an analysis applying aperfect model. The defects are estimated for their ef-fect on the final result, which is then quantified. Thenthese defects are quantified according to the usualconditions of the laboratory. Finally, some kind of“final balance” is established.

– The implementation of this methodology is based ona mathematical equation. This should not deter us [7,11, 12] and the help of a specialist may be asked for ifnecessary. Specialised software can calculate uncer-tainties. The essential part of the exercise is to identi-fy, using one’s own knowledge, the various sources ofuncertainty.

– In the case of reasoning based purely on mathematics,special attention must be given to the fact that uncer-tainty can be over-estimated by calculating the samecontribution twice, such as the uncertainty concerningthe preparation of the standards which is reflected inthe linearity of the calibration line. Parameters whichdo not contribute to the uncertainty, such as the vol-ume of the solvent of a test sample, if it does not con-tribute to the calculation of the result, should not beconsidered as a source of uncertainty. This does notprevent us from having a safety margin, especially foranalysts who lack the experience to perform reliableestimations.

A.4.4. I have read GUM and the EURACHEM guide,but it seems difficult to apply them to all my analyses. Are there steps which I should follow?

The first step should be to order the various analysesmade by the laboratory according to the technical and fi-nancial criticality of the analysis. If an analysis is per-formed every day to check that a value does not exceed alimit of 100 ppm, and results between 10 and 20 ppm arefound throughout the year , it is not urgent to knowwhether the uncertainty is 10 or 20% of the 10 ppm. Pri-ority can be judged as a function of the frequency of theanalysis. However, this criterion may be dangerous whenused alone.

Another step would be to make a provisional estima-tion of uncertainties. There are two ways to achieve this:

– “Batch” estimation: three big batches of sources ofuncertainty can be identified and added.1. Uncertainty related to standards, titrated solution,

certified reference material (CRMs), standard mix-ture diluter, etc.

2. Uncertainty attributable to the protocol: test sam-ple, extraction efficiency, matrix effect, slight in-terferences, etc.

3. “Mathematical” type of uncertainty: to be attrib-uted to linearity, statistics of the series

– “Block” estimation: the operator and supervisor esti-mate the global uncertainty based on their experienceand scientific honesty. The answer may be periodical-ly re-evaluated. This approach will give rise to criti-cism, but it is preferable to ignorance. It may be usedto identify critical points which justify a decrease ofthe uncertainties.

A.4.5. When do we have to proceed to uncertainty estimations?

It is not recommended that the analyst spends much timeevery day, estimating the specific and detailed uncertain-ty on the day, thus indicating that it is 0.93% today, andwas 0.90% or 0.96% the day before. A reasonable ap-proach is to proceed to a standard uncertainty estimationfor each significant phase of the method.

The uncertainty may be evaluated:

– When the method is designed: a provisional uncertain-ty estimation may be recommended when a newmethod is under investigation, based on the experi-ence of the operator and information reported in thescientific literature, apparatus manufacturer documen-tation, and common sense. This first estimation willallow, for instance, the laboratory to note whether theuncertainty limits are achievable or whether it is un-reasonable to start the research. It can also indicate ifthe analysis will be a difficult challenge and thepoints to be careful of.

The whole approach must be extended with a continuousseries of operations, each one with a specified uncertaintyand so on, until the defined units. Furthermore, the adequa-cy of the calibration with the measurement conditionsshould be checked. This is the adequacy of the standard.

The whole approach should be carried out before therealisation of the analysis, since it determines one of itscomponents. This does not mean that each analyst has touse the complete approach on their own. They should es-tablish a link with common bases as soon as possible [13].

B.2. How should we manage traceability to standards?

The methodology to be followed depends on the type ofmethod (and protocol) and on the measurement principleon which it is based. The scientific basis of the analysisshould be known and respected.

There are three types of methods and recommenda-tions identified in ISO Guide 32 [14]: tracing of weigh-tings, ( type I methods), the use of “pure products” (typeII methods), the use of a CRM, or internal referencematerial (RM), which are themselves traceable (type IIImethods).

Good management of this question is favoured if theword “tracing” is given its primary meaning: to establishthe function which relates the signal to the result.

B.2.1. RM or CRM use is often recommended as the bestor even the only means of calibration. Is this correct?

In order to answer this question, a clarification of themeaning of RM and CRM [15] is needed.

If we consider that pure products, standard titrated so-lutions, and of course, composition RMs which repro-duce a given type of matrix are CRMs, this recommen-dation is valid. If RM and CRM are given a restrictivemeaning, only covering the reference materials repro-ducing a matrix, this recommendation will not be appli-cable in many fields where they do not exist.

When RMs are only used to check the reproducibilityof a method, they do not participate in calibration.

B.2.2. Should internal or external means be used to ensure the tracing?

The first answer is to say that both should be used.A function can only be externalised if a reliable ser-

vice is available on the market.Some laboratories ,for whom money is easier to find

than time and knowledge, prefer sub-contracting. Theynevertheless need to plan time internally to identify theirneeds and validate the solutions proposed. For laborato-

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– At the end of the development and validation of themethod : this allows a statement to be made about themetrological quality.

– Then the stability of the conditions in which the un-certainty has already been evaluated should bewatched during the implementation period. In casethere is an evolution, the uncertainty may be re-evalu-ated.

The following factors can induce a significant, favour-able or unfavourable, evolution of the uncertainty:

– Know-how– Modifications of apparatus or consumable items– Method evolution– Operator change– Evolution of the nature of the samples.

Even if none of these factors change, re-examining theuncertainty estimation periodically (each year) is useful,in order to make sure, for instance, that the quality of theanalyses has not been damaged by “fatigue” of the appa-ratus or “drift” of the operator. This can only be a partialexamination related to critical or sensible aspects of theanalysis.

Following the control chart may be useful to identifyevolutions.

B. Chemical analysis should be traced to units

B.1. My method is considered validated; which complementary approach does its tracing to the standard, its traceability correspond to?

This question puts into light the fact that, for the analyst,these two aspects of the problem are closely associated:it is necessary to examine a problem in a systematic andCartesian manner, without forgetting about the back-ground realities and objectives.

The following logic can be used: a chemical analysisis usually carried out with an “analytical system” or“sensor”, which is sensitive to the measurand. This anal-ysis system produces a “signal” which is converted intoa result. To be able to express this analysis result, the re-sponse factor to apply to the “signal” should be known.The standard will not compensate for all the imperfec-tions of the analysis, the operator’s work or the instru-mentation. Tracing the value to units and standards al-lows one to ensure that the response factor is applicableand acknowledged by everyone. Saying “I have a stan-dard solution that I regularly use to check the sensitivity”is not enough. The recognised status of the titre of thesolution with a recognised and appropriate uncertainty aswell as the fact that the titre has been determined using aprocedure which also has a recognised and appropriateuncertainty must be proven.

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ries with less money available, “do it yourself” shouldnot be used more than is reasonable. For very basicneeds, (for example, preparing a mixture of solutions),calls for tenders and orders, etc. are not worthwhile.However, if a partner laboratory can cover means andcompetencies that a laboratory does not have, externali-sing can be a good solution, especially if it is managedas a long-term partnership.

This point will be discussed in Sect. C.

B.2.3. Is it true that the principle of tracing, as applied to physical measurement, is not applicable to chemical analysis?

I am afraid this type of remark is rooted in a partialknowledge of the diversity of the principles implementedin physical units metrology. The particular case of massmeasurement traceability is sometimes wrongly consid-ered as applicable to all fields of physics. It would behard to list all the tracing dispositions implemented inphysical measurement [16, 17].

For example, while consulting what is applied toangle or pressure measurements, interesting similaritiescan be found with chemical analysis and their varioussolutions, which present ideas to work on [18]. There arein fact differences because of the difference in the matu-rity of the market, but these should not be considered asprinciple differences.

B.2.4. Sampling and extraction are sometimes said to break the traceability of a chemical analysis. Is this true?

This type of remark can upset a non-experienced analyst.Such a comment should not be taken as a reason toignore traceability.

When proceeding to sampling or extraction, the basichypothesis is that the sampling is representative and ev-erything needed has been extracted or that the extractionrate is known. Since the reality is not strictly in confor-mity with the basic model, imperfections exist, that is tosay, more uncertainties, but traceability still exists.

Finally, for certain fields of analysis, only the extract-able part is quantified: the measurand is modified, butthere is no break of traceability.

C. Now that the essential motivations and requirements of chemical analysis have beendiscussed, is it possible to examine the concreteand practical application?

The main point is to picture how to apply the principle oftracing to units and standards. The starting point of the

approach is to define the specifications of the standardsand, especially, to specify:

– The uncertainty required– The matrix, its composition and form, on which the

adequacy of the standards are dependent– Some practical consideration (accessibility, cost).

The idea to keep in mind is that if too severe specifica-tions are given for the standard, there is the risk thatwhat is looked for does not exist. Some flexibility mustbe allowed while preparing the specifications list, byordering them according to three criteria: compulsory,desirable or optional.

Non-held specifications can also be classified for therecord.

If no solution complying with the compulsory specifi-cations is found, the whole problem should be re-consid-ered, including the analysis objectives.

Examining the possible solutions of tracing impliesthat the ISO 32 Guide [13] has been read and that themethods have been ordered according to the classes pro-posed in the guide.

Stability of the analysis system is one of the selectioncriteria upon which the choice of the tracing mode is de-pendent. If the system changes from one day to the next,the laboratory needs to re-calibrate it everyday. If thesystem is stable over months or even years, externalmeans can be used for calibration. The latter hypothesisis not usual in the field of chemical analysis.

Another criterion for choosing the mode of tracing is toestablish how the laboratory contributed to the implemen-tation of the solution. This can either mean that the labora-tory does nothing, or it implement itself, all actions.

Practically, a compromise between these two ex-tremes has to be found; it will usually be up to the opera-tor to prepare the dilutions and mixtures necessary tomake the working standards. Pure products, on the con-trary, will not be prepared or controlled by the user, ex-cept if there are specific requirements.

In order to choose between internal and externalmeans, it is useful to examine both scenarios: with out-sourcing and without. If outsourcing provides specialisedmeans that the laboratory does not have and if the expe-rience and results are beneficial to several users, thesemeans are obviously better suited than those of the labo-ratory.

C.1. Could you give some practical examples of elementary and mineral analyses?

Measurands are generally the amount of ions or ele-ments.

If the method is a type II method which implementssamples in solution, standard solutions are used as astandard. The most rational way to get hold of them is to

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buy them from a supplier who can provide proof of theirmetrological traceability. Of course, it is possible to pre-pare them oneself but it will not necessarily be benefi-cial. The purity and stoichiometry of the starting materialand the hydration state of the salts should be taken intoaccount.

If the method is a type III method, the main tracingmode is to use CRM with matrixes similar to those of thesamples analysed. When they are available on the na-tional and international market, the best solution is tobuy them.

Furthermore, even if this possibility has not yet beenfully developed, it may be useful to highlight the devel-opment of primary methods in chemical metrology labo-ratories [18, 19]. These methods allow calibration ofRMs which cover specific needs. Such methods are cost-ly and will only be used in important cases.

C.2. Could you give examples of molecular analyses,especially organic ones?

The measurands are the amount of one molecule, or evenone given isomer.

For type II analysis methods, the standards are stan-dard solutions. Given the number of molecules and ma-trixes, it will be difficult to find them all as titrated solu-tions on the market, so most of the time, the solutionmust be prepared by the laboratory using them.

There are ready to use mixtures in some specialisedfields (for example: pesticides, polycyclic aromatic hy-drocarbons, residue solvents). Ready mixtures are espe-cially interesting when the solutions contain severalcomponents in small amounts and when supplyingand/or manipulating them in a pure state is difficult foran isolated user. In this case, the role of the one in chargeof the accuracy of the solutions titre must be made clear.Special attention must be paid to the purity of the anal-yte. A product with a certified purity with a batch analy-sis certificate is preferable to a stock product which hasundergone limited control. If only the latter is available,the user is responsible for establishing the consequencesof the degree of purity related to the way they use thestandard solution. When a molecule is only produced byone company, the latter must carry out an action in orderto develop its metrology system.

For type III methods, the same recommendations forelementary and mineral analysis are applicable.

C.3. Can you give examples of gas (and vapours) analyses to end this presentation?

These examples will highlight the fact that the nature ofthe tracing means must take into account the characteris-tics of the analytes and matrixes. Gas analysis is differ-

ent in that a precisely dosed mixture is difficult to pre-pare.

The calibration of gas (or vapours) analysers maysometimes be done by an external “calibration laborato-ry”, i.e. manufacturer of the analyser or other specialisedlaboratory. Special care must be taken to check that thework is done according to the state of the art and metrol-ogy rules and that it is not just an imprecise scale settingmade to help out the customer, But good work will haveto be paid for. In general, tracing is done using a stan-dard gas; specialised suppliers sell them ready-for-usewith proof of the metrological traceability [21]. Thesemixtures can also be prepared before use with dynamicpreparation systems using pure gas dilution. These sys-tems should be calibrated for flows. Finally, it is possibleto combine these two solution types by proceeding to ametrological dilution of a high concentration referencemixture.

Buying a gas reference mixture is the best solution fora laboratory proceeding to the analysis of a limited num-ber of matrixes.

On the contrary, dynamic preparation, which is moreflexible but which implies more important material in-vestments, is to be recommended for laboratories whoseactivities are more varied.

C.4. Additional remarks

All the recommendations proposed here correspond togeneral cases. In some particular cases these recommen-dations may not be suitable.

In the previous two paragraphs, the uncertainty of thevarious proposed means and methods has not been men-tioned. This has been done on purpose because it wouldhave led to the development of this section beyond itsaim. Furthermore, it could have led readers to believethat certain methods automatically carry certain levels ofuncertainty, which is not true.

It is up to each user to evaluate the uncertainty oftheir standards, at the time of choosing them, and thenwhen using them. Consulting the national metrology lab-oratories’ web sites [16] , will help.

There are uncertainties examples in the literature,which may also be useful, especially in ACQUAL.

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Bibliogaphy for French-speaking readers

English speaking readers may refer to the bibliography given in Chapter 7 of Günzler H (1996) Accreditation and quality assurance in analytical chemistry. Springer Berlin Heidelberg New York

1. Marschal A, Andrieux T, CompagonPA, Fabre H (2001) STP Pharma Prati-ques 11: 13–20

2. NF X-07–0011 (1994) Normes fond-amentales, Vocabulaire internationaldes termes fondamentaux et générauxen métrologie, (VIM). ISO, Geneva,Switzerland

3. Potier A, et al. (1999) STP PharmaPrat 2: 141–159

4. Marschal A (1980) Bulletin du BureauNational de Métrologie. 39: 33–39

5. Afnor (ed) (1996) Métrologie dansl’entreprise, outil de la qualité. MFQ,

6. Gy P. – Echantillonnage. – Techniquesde l’ingénieur, traité Analyse et Carac-térisation, p 220

7. NF X 07–021 (1999) Normes fond-amentales. Métrologie et applicationsde la statistique. Aide à la démarchepour l’estimation et l’utilisation del’incertitude des mesures et des résul-tats d’essais

8. NF ENV 13005 (1999) Normes fond-amentales. Guide pour l’expression del’incertitude de mesure

9. (1999) Vingt-sept exemples d’évalua-tion d’incertitudes d’étalonnage. – Ed. Mouvement français pour laqualité

10. EURACHEM-CITAC (2000) Quanti-fying uncertainty in analytical mea-surement, 2nd ed. EURACHEM, Teddington, England

11. Ranson C (1996) Bulletin du Bureaunational de métrologie 103: 13–17

12. Perruchet C, Priel M (2000) Estimerl’incertitude. Mesures et essais– Ed. Afnor

13. Marschal A 1994) Traceability and cal-ibration in analytical chemistry. ProcSymposium EUROLAB, Florence

14. ISO Guide 32 (1997) Etalonnage enchimie analytique et utilisation desmatériaux de référence certifiés. ISO,Geneva, Switzerland

15. Guide ILAC-G9 (1999) Problèmatiquede la sélection et de l’utilisation desMRC. – Publié en français par le Cofrac,16 janv-mars

16. Blouet J (1997) Bulletin du Bureau na-tional de métrologie 107: 1–132

17. (1997) Etalons et unités de mesure. – Bureau national de métrologie

18. Muijlwijk R (1999) Accred Qual Assur4: 477–478

19. Labarrage G, Marschal A, Sigala M(1999) Bulletin du Bureau national demétrologie 115: 39–47

20. Milton M, Marschal A (2001) AccredQual Assur 6: 270–271

21. Barbe J (1997) Bulletin du Bureaunational de métrologie 109: 25–30