the general aim of analytical chemistry is to make

M. Valcárcel Metrology in Chemistry

1

B. Neidhart, W. Wegscheider (Eds.): Quality in Chemical Measurements © Springer-Verlag Berlin Heidelberg 2000

METROLOGYIN

CHEMISTRY

ANALYTICAL CHEMISTRY-QUALITYBINOMIAL GENERAL ASPECTS

PRACTICALAPPROACHES

FINALREMARKS

PRINCIPAL DIFFERENCESBETWEEN

PHYSICAL AND CHEMICALMEASUREMENTS


2


C

SYNTHESIS

APPLICATIONSTHEORY

ANALYSIS

AN INFORMATION SCIENCE

ANALYTICAL CHEMISTRY

THE DISCIPLINE OF CHEMICAL MEASUREMENTS

THE CHEMICAL METROLOGICAL DISCIPLINE


3


THE GENERAL AIM OF ANALYTICAL CHEMISTRY IS TO MAKETHE INTRINSIC BUT LATENT INFORMATION ON AN OBJECTEVIDENT, MEASURABLE, TRUTHFUL AND USEFUL

INFORMATION

CHEMICAL

EVIDENTMEASURABLE

AVAILABLE

LATENTINTRINSIC

USEFULTRUTHFUL

IDENTIFICATION ORIGIN

CHARACTERIZATION

QUALITY

APPLIEDBASIC

TECHNICAL


4


THE MAIN GOAL OF ANALYTICAL CHEMISTRY IS TO MINIMIZEUNCERTAINTY ON THE CHEMICAL INFORMATION OF A OBJECT

OR A SYSTEM

THREE TYPES OF CHEMICAL INFORMATION

ANALYTICALINFORMATION

ROUTINELYPRODUCED

REALQUALITY

INFORMATIONCONSIDEREDTO BE TRUE

AC

CU

RA

CY

UNCE

RTAI

NTY

REFERENTIALQUALITY

INTRINSICINFORMATION

IDEALQUALITY TRUENESS


5


BASIC FACET

QUALITY

APPLIED FACET

ATTRIBUTESCHARACTERISTICS

FEATURES

SATISFACTIONOF CLIENT

REQUIREMENTS

ANALYTICALPROPERTIES

ANALYTICALPROBLEMS

SOLVING

ANALYTICALCHEMISTRY

METROLOGYIN CHEMISTRY

COHERENCE BETWEENREQUESTED AND

DELIVERED CHEMICALINFORMATIONS


6


REFERENCES FORANALY TICAL QUALITY

QUALITY COMPARISON

TO WHAT?

MEASUREMENTSTANDARDS

INTANGIBLESTANDARDS

NORMS / GUIDES, etc

CHARACTERISTICSOF THE CLIENT'S

INFORMATION NEEDS

METROLOGICALQUALITY

ANALYTICALPROBLEMSOLVING

BASICFACET

ANALYTICALQUALITY

APPLIEDFACET


7


TRACEABILITYANALYTICALPROBLEMS

SOLVINGPROPERSAMPLING

RAPIDITY,COSTS,

etc

COHERENCE BETWEENDELIVERED AND

REQUESTEDINFORMATIONS

QUALITY OFANALYTICAL

INFORMATION

THE HYDRODYNAMIC MIXING MODEL OFTHE INTEGRAL ANALYTICAL QUALITY

METROLOGICALQUALITY

REPR

ESEN

-

TATI

VENE

SS

ACCU

RACY

FITNES

SFO

RPU

RPOSE

LOW

UNCE

RTAI

NTY


8


ISMETROLOGY

IN CHEMISTRY

UNDER THE RESPONSIBILITYOF ANALYTICAL CHEMISTRY?

THE EXCLUSIVE GOAL OFANALYTICAL CHEMISTRY?

RELATED TO THE FOUNDAMENTALSOF ANALYTICAL CHEMISTRY?

RELATED TO THE QUALITYOF THE ANALYTICAL INFORMATION?

DIRECTLY

YES

YES

YES

YES

NO

NO

INDIRECTLY

RELATED TOFITNESS FOR PURPOSE?


9


NATUREOF

MEASUREDPARAMETERS

PHYSICAL


CLASSICAL

PHYSICO-CHEMICAL

CHEMICAL BIOCHEMICAL

BIOLOGICAL


10


METROLOGY IN CHEMISTRY

MEASUREMENTS OF (BIO)CHEMICALPARAMETERS

COMMON BASIC PRINCIPLES

DIFFERENT PRACTICALCONNOTATIONS

AS REGARDS:

METROLOGY IN PHYSICSIN BIOLOGY


11


PHYSICALMEASUREMENTS

BASIC PRINCIPLES OF METROLOGY

CHEMICALMEASUREMENTS

BIOLOGICALMEASUREMENTS


APPLIED FACETS OF METROLOGY


BIOLOGICALMEASUREMENTS


12


METROLOGYIN

CHEMISTRY

PHYSICAL

CHEMICAL

BIOLOGICAL

BIOCHEMICAL

PHYSICO-CHEMICAL

NATURE OFMEASURED

PARAMETERSBASIC

PRINCIPLES

RELEVANT DIFFERENCES FROM APRACTICAL POINT OF VIEW

DEGREE OFDIFFICULTY

TO PERFORMRELIABLE

MEASUREMENTS

AVAILABILITYOF PROPER

MEASUREMENTREFERENCES


13


ANALYTICAL CHEMISTRY,TOMORROW

SYSTEMATIC TREATMENT ASINFORMATION SCIENCE

TO PROPITIATEQUALITY DEVELOPMENTS

EXPLORATION OF ITSMETROLOGICAL CHARACTER

AUTOMATIZATION,MINIATURIZATION, SIMPLIFICATION

RESPONSIVEANALYTICAL TOOLS

TOOLS

PROCESSES

EXPANDING BOUNDARIES

MORE EMPHASIS ON THEANALYTICAL PROBLEM

NEW PEDAGOGICALAPPROACHES

ANALYTICAL QUALITY

GENERIC

B A S I C

SPECIFIC

T R E N D S

DISTINCTIONINTRINSIC AND SHARED

FOUNDAMENTALS


14


TRADITIONALAPPROACH


CHANGES

POSITIVE EVOLUTION TO BASICANALYTICAL QUALITY

ANALYTICAL CHEMISTRY IS BOTHTECHNICALLY AND SCIENTIFICALLYENRICHED (no crucial innovations arereally introduced)

OLD PRINCIPLES DO NOT DISAPPEAR;RATHER THEY ARE IMPROVED

METROLOGICALAPPROACH


15


TRADITIONALAPPROACH


ACCURACY

PRECISION

STANDARD,OFFICIAL ...METHODS

TRACEABILITY

UNCERTAINTY

PRIMARYMETHODS

TRACEABLEMETHODS


16


TRADITIONALAPPROACH


GLOBAL INTERESTON THE ANALYTICAL

PROCESS

NON-SYSTEMATICGENERICINTEREST

ON QUALITY

LITTLE ATTENTIONPAID TO OTHERLABORATORIES

EMPHASIS ON

IMPLEMENTATION OFQUALITY SYSTEMS

(QA, QC, QA)

MORE EMPHASISON REFERENCES

(measurementsstandards)

MORE EMPHASIS ONTHE QUALITY OFMEASUREMENTS

- COMPARABILITY- HARMONIZATION


17


CHEMICALMEASUREMENT

PROCESSES

BETWEEN

TO OUTLINE THEINTRINSIC

FEATURES OFMETROLOGY IN

CHEMISTRY

TO DEMONSTRATE THENEED OF SPECIFIC

DEVELOPMENTS OFMETROLOGY IN CHEMISTRY

IMMEDIATEEXTRAPOLATIONSARE GENERALLY

WRONG ANDDANGEROUS

NORM, GUIDESAND DICTIONARIES

ARE STRONGLYBASED BY THE

TRADITIONON PHYSICAL

METROLOGISTS

TO LEARN FROM ANDTAKE ADVANTAGESOF DEVELOPMENTS

IN PHYSICAL (CLASSICAL)METROLOGY IN ORDER

TO CAREFULLY ADAPT THEMTO CHEMICAL METROLOGY

PHYSICALMEASUREMENT

PROCESSESCMPs

AS A WAY

ESTABLISHING THE MOST RELEVANTDIFFERENCES

PMPs


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DIFFERENCES BETWEEN CHEMICAL (CMPs) ANDPHYSICAL MEASUREMENT PROCESSES (PMPs)

CMPs ARE STRONGLY SAMPLE-DEPENDENTPMPs ARE VIRTUALLY SAMPLE-INDEPENDENT

QUITE SIMILAR PMPs CAN BE APPLIED TO MEASURE

THE LENGTH OF A TABLE

I

THE HEIGHT OF A TREE THE DISTANCE BET-WEEN TWO OBJECTS

DIFFERENT CMPs (MAINLY THE FIRST STEP) MUST BEAPPLIED FOR THE DETERMINATION OF A PESTICIDE IN

WATERS (from spring to waste waters)

SOILS

SEDIMENTS

PLANTS

BIOLOGICAL FLUIDS

COMMERCIALLY AVAILABLE FORMULATIONS

SOILS


19



II

AS A CONSEQUENCE OF

MILLIONSOF

CHEMICALSPECIES

THOUSANDSOF

SAMPLE TYPES

PRACTICAL LIMITATION OFMETROLOGY IN CHEMISTRY

FEW GENERAL CMPs AREAVAILABLE

COMBINATION

CMPs ARE HIGHLY VARIED; BY CONTRAST,THERE ARE LESS PMPs WHICH ARE MORE GENERAL


20



III

PO

PRELIMINARYOPERATIONS

OFMEASURINGPROCESSES

IN

CMPs

PMPs

GREAT IMPACT

CMPs

GREAT SIGNIFICANCE

LITTLE IMPORTANCE

FROM A PRACTICAL POINT OF VIEW

ON THE QUALITY OF RESULTS

SAMPLE

RANDOMSYSTEMATIC ERRORS

- TEDIOUS- TIME-CONSUMING

- SOURCE OF

- HAZARDS FOR ANALYST AND ENVIRONMENT

RESULTS

PMPs

MEASURING ANDTRANSDUCING

THE SIGNAL

DATAHANDLING

ANDTREATMENT

PRELIMINARY OPERATIONS RESULTS

MEASURING ANDTRANSDUCING

THE SIGNAL

DATAHANDLING

ANDTREATMENT


21



IV

PMPs RELY ALMOST EXCLUSIVELYON DIRECT-USE INSTRUMENTS

MEASUREMENT EQUIPMENT ARE NOTTHE SOLE FOCUS IN CMPs: MANY

OTHER FACTORS AFFECT THE QUALITYOF RESULTS


22



V

SAMPLING

HETEROGENEITY OF OBJECTS AND SAMPLESINTRODUCES SERIOUS ERRORS IN CMPs

THIS PROBLEM IS ALMOST EXCLUSIVE OFMETROLOGY IN CHEMISTRY

KEY ASPECT IN CMPs TOASSURE REPRESENTATIVENESS

DOES NOT EXIST ORIS QUITE SIMPLE IN PMPs


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5-20% OF THE NEEDS FOR APPROPRIATEMEASUREMENT STANDARDS HAVE BEEN MET

FOR CMPs; COMPARED WITH 80-90% FOR PMPs

VI

WITHOUT QUALITY REFERENCESANALYTICAL CHEMISTRY MAKES NO SENSE

APPROPRIATE REFERENCES IN METROLOGY IN CHEMISTRYARE NOT ONLY CALIBRANTS (AS IN PMPs), BUT

ALSO MATRIX-TYPE (CERTIFIED) REFERENCE MATERIALS

NEED FOR A HIGH NUMBEROF REFERENCES OWING TOTHE GREAT VARIETY OF CMPs

PROBLEM:

DEVELOPMENTOF STANDARDS

HOT RESEARCH TOPICOF ANALYTICAL CHEMISTRY

NEED TO DEVELOPRELIABLE ALTERNATIVESTO ASSURE THE QUALITY

OF RESULTS

STANDARDADDITIONMETHOD

INTERLABORATORYEXCERCISES

MORE PROMINENTROLE IN CMPs


24



VII

UNLIKE IN PMPs, IN CMPs MEASUREMENTSTANDARDS ARE NOT EXCLUSIVELY

USED FOR CALIBRATING INSTRUMENTS

USE OF MEASUREMENTSTANDARDS INMETROLOGY

EQUIPMENTCALIBRATION

METHODOLOGICALCALIBRATION

GLOBALEVALUATION

OTHERS

METROLOGYIN PHYSICS

METROLOGY

IN

CHEMISTRY


25



VIII

IN PMPs IS EASIER TO ACHIEVE TRACEABILITYBECAUSE OF:

- AVAILABILITY OF TRANSFER STANDARDS- SIMPLICITY OF THE PROCESSES

BY CONTRAST, TRACEABILITY IN CMPs IS AMETROLOGICAL CHARACTERISTIC DIFFICULTTO BE DEMONSTRATED IN AN ORTHODOXWAY (definition of traceability in the metrologicaldictionary)

THE ORDINARY LAST REFERENCE IN THECHAIN OF COMPARISONS SUPPORTING THETRACEABILITY OF A RESULT IS AN SI UNIT

METROLOGY IN PHYSICS

THE LAST REFERENCE OF THE TRACEABILITYCHAIN CAN BE

- SI UNIT (the kg or the mole)- WELL-STATED STANDARDS (CRM, RF, ...)- PRIMARY METHODS- SPECIALIZED LABORATORIES OF EXCELLENCE- GROUP OF LABORATORIES (proficiency testing)



26



IX

THE STANDARDS USED IN PMPs ARE, IN GENERAL,HOMOGENEOUS (except SI units); BY CONTRAST

THOSE USED IN CMPs ARE QUITE HETEROGENEOUS

METROLOGYIN

PHYSICS

SI UNIT

NATIONALSTANDARDS

REFERENCELABORATORY

STANDARD

LABSTANDARD

METROLOGYIN

CHEMISTRY

SI UNIT

CHEMICALSTANDARDS

ANALYTICALSTANDARDSPRIMARY

SECONDARY


27


EXAMPLE

TITRIMETRIC DETERMINATION OF CL2 (OXIDANT)

Kg / MOLE

ATOMIC WEIGHTS(I, O, K, S, Cl

KIO3

SIUNITS

CHEMICALSTANDARDS

ANALYTICALSTANDARDS

STOICHIOMETRY

S2O32-

ANALYTICAL

STANDARDS

TITRIMETRY

PRIMARY

1st step IO3- + 5I- + 6H+ 3I2 + 3H2O

2nd step I2 + 2S2O32- S4O6

2-

SECONDARY

ANALYTE

1st step Cl2 + 2I- 2Cl- + I2

2nd step I2 + S2O32- S4O6

2- + 2I-

BURETTE

IO3- - 3 I2 - 6S2O3

2- - 6I2 - 6Cl2


28


BIPM

NON ACCREDITATEDLABORATORIES

NATI

ONAL

METROLOGI CAL LABORATORIES


X

THE EXISTENCE OF A WELL-ESTABLISHEDNATIONAL AND INTERNATIONAL NETWORKOF PHYSICAL LABORATORIES IS A GREAT

ADVANTAGE OF METROLOGY IN PHYSICS, THATIN FACT DOES NOT EXIST IN CHEMISTRY


29



XI

THE PRACTICAL APPROACH TO UNCERTAINTYIN CMPs AND PMPs IS QUITE DIFFERENT

PHYSICAL


THE CLASSICAL APPROACH TO CALCULATEUNCERTAINTY IN METROLOGY INPHYSICS CAN NOT BE DIRECTLY

APPLIED IN CHEMICAL MEASUREMENTS

TYPE OFERRORS



BIAS

RANDOM

- PREDOMINANT- CORRECTABLE

- SMALLER

DIFFICULT TOIDENTIFY AND ERADICATE

PREDOMINANT

ENTIRELYDIFFERENT

ERRORPATTERNS

BEHAVEDIFFERENTLY

OF REPLICATION


30



XII

QUALITATIVE ANALYSIS IS A DISTINCTASPECT OF METROLOGY IN CHEMISTRY

AS IT DOES NOT ALMOST EXIST INMETROLOGY IN PHYSICS

THE BINARY YES/NO RESPONSEIS CRUCIAL IN TODAY'S AND

TOMORROW ANALYTICAL CHEMISTRY

THERE IS A NEED TO DEVELOPSPECIFIC

METROLOGICAL PRINCIPLESIN

QUALITATIVE ANALYSIS

IDENTIFICATION

HYBRIDATION

RESPONSIVEANALYTICAL

SYSTEMS

POWERFULSEPARATIONTECHNIQUES

POWERFULIDENTIFICATION

TECHNIQUES


31


PRACTICALAPPROACHES

TO


THE FRAMEWORK OF ANALYTICALCHEMISTRY-QUALITY BINOMIAL

ITS INHERENT FEATURES

THE DIFFERENCES BETWEEN

TAKING INTOACCOUNT

CMPsPMPs


32


SAMPLINGPRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRYUNCERTAINTYCALCULATIONSCALIBRATION LASTREFERENCEIN THETRACEABILITYCHAIN INTERNALQUALITYCONTROLVALIDATIONPROFICIENCYTESTING I

SAMPLING

PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY

UNCERTAINTYCALCULATIONS

CALIBRATION LASTREFERENCE

IN THETRACEABILITY

CHAIN

INTERNALQUALITY

CONTROL

VALIDATION

PROFICIENCYTESTING

I


33


PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY II

SAMPLING

PRELIMINARY OPERATION OF CMPs THATCAN SIGNIFICANTLY CONTRIBUTE TO

THE UNCERTAINTIES OF RESULTS

NEED TO SYSTEMATICALLY CONSIDERSAMPLING IN QUALITY SCHEMES,

NORMS, GUIDES CONCERNING METROLOGYIN CHEMISTRY


34


PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY III

UNCERTAINTYCALCULATIONS

UNCERTAINTY IS A KEY ASPECT OF TRACEABILITY:IT IS NECESSARY TO IDENTIFY ALL SOURCES OFUNCERTAINTY

MAIN APPROACHES TO QUANTIFYING UNCERTAINTYIN CHEMICAL ANALYSIS

BOTTOM-UP APPROACH- Guide to the Expression of Uncertainty in Measurements (1995) ISO- Quantifying Uncertainty in Analytical Measurement (1995) EURACHEM

see next transparency

FAR FROMTHE REALITYIN CHEMICAL

MEASUREMENTS

GLOBAL APPROACH

OTHERS


35


GLOBAL APPROACH TO CALCULATEUNCERTAINTIES OF CMPs

CRM

U = U + U2 2 2TOTAL SAMPLE PROCESS

REPLICATES

S

S

S

.

.

.

S

1

2

3

n

results U

results U

results U

results U

S

S

S

S

1

2

3

n

RESULTS UPROCESS

USAMPLE


36


PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY IV

CALIBRATION

ESSENTIALASPECT OF

ANALYTICALQUALITY

KEY ELEMENTOF THE UNBROKEN

CHAIN OF COMPARISONS(TRACEABILITY)

DIRE

CT IN

FLU

ENCE

ON

UNC

ERTA

INTY


PLAY ANIMPORTANT

ROLE

DISTINCTFEATURES

IN CMPs

ALLOWS THECLASSIFICATION

OF CMPs

SUBSTANTIALELEMENT

OF METHODVALIDATION

TWO TYPES OFCALIBRATIONPROCEDURES


37


DEFINITION

AIM


ANALYTICALCALIBRATION

CHARACTERIZING THEINSTRUMENTAL RESPONSE

IN TERMS OF ANALYTEPROPERTIES

TO ESTABLISH AN UNEQUIVOCALRELATIONSHIP BETWEEN SIGNALSAND ANALYTE CHARACTERISTICS

FOR BOTH QUALITATIVE ANDQUANTITATIVE PURPOSES

CONTAIN THE ANALYTEEXCEPT IN FACTORING

(TITRIMETRY)

EQUIPMENTCALIBRATION

CHECKING THE CORRECTOPERATIONS OF AN

INSTRUMENT OR APPARATUS

EQUIPMENT

TO CORRECT THEINSTRUMENT RESPONSE

OF THE PARAMETRICREACTING OF AN

APPARATUS

DO NOT CONTAINTHE ANALYTE

P M P s

C M P s


38


CALIBRATION IN CMPs

MOLECULAR UV-VISIBLE ABSORPTION SPECTROSCOPY

EXAMPLE

INSTRUMENTALCALIBRATION

SPECTROPHOTOMETERIN GENERAL

QUANTI-

TATIVE

QUALI-TATIVE

SPECTROPHOTOMETERIN A GIVEN CMP

STANDARDS OF THE TARGET ANALYTE FORESTABLISHING AN ABSORBANCE/CONCEN-TRATION RELATION

ABSORBANCESTANDARDS

WAVELENGTHSTANDARDS

(e.g. potassium dichromatesolution)

(e.g. holmium filter)

e.g. Fe solution for constructing thecalibration curve. The CMP is basedon the formation of the soluble colouredchelate between iron (II) and phenanthroline

++

METHODOLOGICALCALIBRATION


39


TYPES OF CMPs (ACCORDING TO ANALYTICALCALIBRATION) FOR QUANTITATIVE PURPOSES

ABSOLUTEMETHODS

GRAVIMETRYCOULOMETRY

CANDIDATES TO BEPRIMARY METHODS

IDMSTITRIMETRY

CALCULABLE

ANALYTICAL STANDARDS

METHODSUSING


INTEREXTRAPOLATION

METHODS

COMPARABLEMETHODS

RELATIVE

CHEMICAL STANDARDS

BASIC STANDARDS

FLUORIMETRYCHROMATOGRAPHY

X-RAYFLUORESCENCESPECTROSCOPY


40


PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY V

TRACEABLE TO WHAT?

LAST REFERENCEIN THE TRACEABILITY

CHAIN

IDEALORTHODOX

ALTERNATIVES

CENTREOF

EXCELLENCE(laboratory

of reference)

REAL

WELL-STATEDMEASURINGSTANDARD

(CRM, RM, ...)

BASICSTANDARD

(SI UNIT)

PRIMERYMETHOD

GROUP OFLABORATORIES

(proficiencytesting)


41


PRACTICAL APPROACHES TOMETROLOGY IN CHEMISTRY V

V A L I D A T I O N

THE TWO FACETSOF ANALYTICAL

QUALITY AREINVOLVED

TO ASSURE

ALTHOUGH METHOD VALIDATION IS THE MOST PROMINENT ACTION IN THISCONTEXT; THERE ARE OTHER APPLICATIONS SUCH AS "DATA VALIDATION","SOFTWARE VALIDATION", etc.

THERE IS A NEED TO ESTABLISH A HIERARCHY IN THIS CONTEXT.

METROLOGICALQUALITY

FITNESS FORPURPOSE

INSTRUMENTSVALIDATION

APPARATUSVALIDATION

VALIDATIONOF

EQUIPMENTS

VALIDATIONOF ANALYTICAL

TOOLS

VALIDATION OFMETHODOLOGIES

VALIDATIONOF

SAMPLING

DATAVALIDATION

VALIDATIONOF

COMPUTERS

VALIDATIONOF REAGENTS,

RMs, etc.

MECHANISMVALIDATION

HARDWAREVALIDATION

SOFTWAREVALIDATION

FIRSTLEVEL

SECONDLEVEL

THIRDLEVEL

FOURTHLEVEL


42


ORTHODOX

(ANALYTICAL)CHEMISTRY

BASIC PRINCIPLESOF METROLOGY

AS REGARDSTHE PRACTICALCONNOTATIONS

OF (TRADITIONAL)METROLOGY IN

PHYSICS

METROLOGYIN

CHEMISTRY

HETERODOX


43


TRENDS INMETROLOGY IN CHEMISTRY

SPECIFIC NORMS, GUIDES, PROTOCOLS ANDDICTIONARIES ARE NEEDED

IN METROLOGY IN CHEMISTRY

INCREMENT OF THEAVAILABILITY OF LOOKING FOR

ALTERNATIVESTO ASSURE THEMETROLOGICAL

QUALITY OFANALYTICAL RESULTS

ESTABLISHMENTOF THE TRACEABILITY CHAIN

FOR THE MOST COMMONCMPs

DEVELOPMENTOF MORE RATIONAL

PROCEDURES TO ESTIMATEUNCERTAINTIES IN

CHEMICAL MEASUREMENTSCONSIDERATION

OF SAMPLINGAS A DECISIVE

ACTIVITYIN METROLOGYIN CHEMISTRY

CENTRES OFREFERENCES

IN SPECIFIC AREASOF CHEMICAL ANALYSIS

SHOULD BE ESTABLISHEDAND RECOGNIZED

METROLOGYOF THEBINARY

RESPONSE

PROMOTION OFMETHOD VALIDATION

INTERLABORATORYEXCERCISES

PROFICIENCYTESTING

REFERENCESUBSTANCES

MATRIX-TYPECERTIFIED

REFERENCEMATERIALS

the general aim of analytical chemistry is to make

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