Bem vindo !

Professor Lindquist, in a seminar on compulsive thinkers, illustrates his brain-stapling technique

Institute for National Measurement Standards

National ResearchCouncil Canada

Conseil nationalde recherches Canada

Traceability, Uncertainty and Reference Materials: New Challenges for the Global Analytical Community

Global Structure of Metrological Measurementsin Analytical Chemistry

Metrology:the science of measurement

P. De. Bievre, Accred. Qual. Assur. (2005) 5: 423-428

is a scientific discipline which develops and applies methods, instruments and strategies to obtain information on the composition and nature of matter in space and time, as well as on the value of these measurements, i.e. their uncertainty,validation and traceability to fundamental standards

Analytical chemistry:

Measurement:set of operations having the object of determining a value ofa quantity: to compare an unknown value to a known value of the same quantity

currently under revision

VIM

Why Analyse ?

The primary purpose in performing analysis is to obtain information that can be used as the basis for making informed decisions.

Accurate and Reliable Measurements:

• ensure equity in domestic and international trade• support responsible government decision making• advance academic research• facilitate inter-operabiliy of components in industry

Comparability of Measurements

consider the Boeing 777:

• comprises 3 million parts• provided by more than 900 suppliers• supplied from 17 countries

…….what could possibly go wrong !

Benefits of Metrological Measurements

... 5% of the GDP of industrialized countries may be associated with the costs of measurements

... up to 30 % of chemical measurements are unfitfor their purpose and need to be repeated

B. King, LGC, 1990

cost savings

• definition of the measurand• another comparative measurement • units of measurement• statement of uncertainty• traceability of the result

By itself, a measurement is worthless !!

To realize its potential worth it needs:

units come from standardsCsample = Cstd (Rsample / Rstd)

Measurement Result …

0.0270.027 Mn in wheat flour0.027 mg/kg Mn in wheat flour0.027 ± 0.003 mg/kg Mn in wheat flour0.027 ± 0.008 mg/kg (U, k=2) Mn in wheat flour0.027 ± 0.008 mg/kg (U, k=2) Mn in wheat flour;

traceable to the SI through standards held at the NRC

a traceable analytical measurement

“the property of the result of a measurement or the valueof a standard whereby it can be related to stated references, usually national or international standards, through anunbroken chain of comparisons, all having stated uncertainties”

Traceability

traceability enables comparison of measurement results

Traceability chain:

a chain of successive comparisons (i.e., measurements) ofone value to another value which ends in the value of the unit chosen to express the result of the measurement

Impact of Traceability

- the ability to produce valid analytical data with stated uncertainty

- to have an anchor point (stated reference) to pin that data to,so that it can be compared with data generated at anotherplace and point in time

The Convention of the Metre

Signed in Paris in 1875by representatives of 17 nations. As well as founding the BIPM

currently 51Member States

Metre ConventionMetre Convention

1875

General Conference on Weights and Measures( CGPM )

meets every four years and consistsof delegates from Member States

International Committee for Weights and Measures ( CIPM ) consists of eighteen individuals elected

by the CGPM It is charged with supervision of the BIPM

and affairs of the Metre Convention The CIPM meets annually at the BIPM

DiplomaticTreaty

Associate Statesand Economies

of the CGPM

Governmentsof

Member States

Internationalorganizations

Consultative Committees( CCs )

Ten CCs each chaired by a member of CIPM;to advise the CIPM; act on technical matters and

take important role in CIPM MRA; compriserepresentatives of NMIs and other experts.

Nationalmetrologyinstitutes( NMIs )

CIPMMRA

Bureau International des Poids et Mesures( BIPM )

International centre for metrology

Laboratories and offices at Sèvreswith an international staff of about seventy

Pavillon de Breteuil

BIPM

global organization for dissemination of the SI

coordinating andpromoting thedevelopment of metrology cooperationwith other relevantintergovernmental andinternational organizations

The SImol - amount of substancem - lengthkg - masss - timeA - currentK - temperaturecd - luminous intensity

The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol".

When the mol is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

The international measurement system was agreed upon in 1960 as the SI

THE OTTAWA CITIZEN FRIDAY, JANUARY 12, 2007Adopting Global Units…

Ottawa Citizen: January, 2007

The CIPM MRA has been signed by representatives of 67 institutes from 45 Member States, 20 Associates of the CGPM, and 2 international organizations (IAEA and EC) – and covers a further 117 institutes designated by the signatory bodies.

Another 100 years later…

Mutual Recognition Arrangement

• drawn up by the CIPM under the Meter Convention• signed October 21, 1999 in Sèvres by Directors of NMIs

and the Transnational Measurement Institute of theEuropean Commission (IRMM)

Goals:declarations of the Degree of Equivalency by NMIsand mutual recognition and acceptance of nationalmeasurement standards

How:signatory participation in Key comparisons of the CCQM or Regional Metrology Organizations and based on achieved performance

NRC Institute for National Measurement Standards

The National Metrology Institute – NMI

national institute designated by the Government (by law) to be in charge of the realization and maintenance of the national measurement standards and the dissemination of traceability

Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO) Rio de Janeiro

Signed in Paris in 1875by representatives of 17 nations. As well as founding the BIPM

currently 51Member States

the MRA(1999)

Metre ConventionMetre Convention

1875

General Conference on Weights and Measures( CGPM )

meets every four years and consistsof delegates from Member States

International Committee for Weights and Measures ( CIPM ) consists of eighteen individuals elected

by the CGPM It is charged with supervision of the BIPM

and affairs of the Metre Convention The CIPM meets annually at the BIPM

DiplomaticTreaty

Associate Statesand Economies

of the CGPM

Governmentsof

Member States

Internationalorganizations

Consultative Committees( CCs )

Ten CCs each chaired by a member of CIPM;to advise the CIPM; act on technical matters and

take important role in CIPM MRA; compriserepresentatives of NMIs and other experts.

Nationalmetrologyinstitutes( NMIs )

CIPMMRA

Bureau International des Poids et Mesures( BIPM )

International centre for metrology

Laboratories and offices at Sèvreswith an international staff of about seventy

Metrology: - Needs and Impacts

crucial issues for society and legislators with large economic, trading and industrial consequences

save $4 billion per year in minimizing TBT

Let’s explore some of these concepts in more detail …..

Each of these quantity values naturally has its own metrologicaltraceability chain by the very fact that it was measured, i.e., compared with another quantity value. These chains also end in a metrological reference, which can be stated.

measurement comparisons

Accred Qual Assur (2004) 10:64P. De BièvreA. Williams

Basic features of a chemical measurement

- validation- comparability- traceability- uncertainty

A measurement result arises from an equation

y = f (x1, x2, …. xm)

which is assumed to hold under certain conditions

y is traceable to x1…xn

xm+1, xm+2…xn

for y to be fully traceable: x1…xn must be traceable to the SI

or themselves be defined values

Consider two laboratories making measurements….

RMtest

sampleA

B testsample

CM

CM

x1

x2

Result y1

y1 = f1(x1)

Result y2

y2 = f2(x2)

y1 is traceable to x1….

y2 is traceable to x2….

there is no basis for comparing y1 and y2

CRM

RMtest

sample

testsample

CM

CM

x1

x2

Result y1

y1 = g1(x0)

Result y2

y2 = g2(x0)

Consider two laboratories making measurements….

y1 and y2 are now traceable to the same reference x0

x0

Traceability in Chemical Measurement

EURACHEM / CITAC GUIDE

2003

The property of the result ofa measurement or the value ofa standard whereby it can be related to stated references,usually national or internationalstandards, through an unbroken chain of comparisonsall having stated uncertainties

Traceability

A guide to achieving comparable resultsin chemical measurement

Traceability is about...• values of measurement results• values linked in a chain by measurement operations• chain consists of comparisons of one value to another• a chain of comparisons of values to an accepted value• final comparison ends with the chosen (defined) value of the unit • chain gives rise to uncertainties because of measurements• chain is a prerequisite for establishment of an uncertainty budget

traceability is not related to a method, an instrument, a material or to an NMI, but always to another value

large uncertainties in links and values

large uncertainty budgets

International Organization of Legal MetrologyOIML

International Union of Pure and Applied PhysicsIUPAP

International Union of Pure and Applied ChemistryIUPACInternational Organization for StandardizationISO

International Federation of Clinical ChemistryIFCC

International Electrotechnical CommissionIEC

Bureau International des Poids et MesuresBIPM

Uncertainty of Measurement Results

GUM

parameter associated with the result of a measurement that characterizes thedispersion of the values that could reasonably be attributed to the measurand

xi xj xk

y = f (xi, xj, xk) y

+ +

Practical Traceability - Uncertainty

measurement uncertainty is easy if the model is complete

Ellison and Williams, Accred, Qual. Assur.(2003) 8: 483-485

A Type A evaluation of standard uncertainty is based on any valid statistical method for treating data; e.g., calculating the standard deviation, fit a curve to data, ANOVA,etc. to identify and quantify random effects in measurements.

the standard uncertainty u(xi) associated with xi is the estimated standard deviation of the mean

Uncertainty of Measurement Results

n

xi = Xi = Σ Xi,kk=1

1n

u(xi) = s(Xi) = Σ ( Xi,k – Xi) 2k=1

n1n (n-1)

½( (

A Type B evaluation of standard uncertainty is obtained bymeans other than statistical analysis of series of observationsusing scientific judgment and information, which may include:

• previous measurement data• experience with, or general knowledge of, the behavior and

property of relevant materials and instruments• manufacturer's specifications • data provided in calibration and other reports • uncertainties assigned to reference data taken from handbooks

uncertainty is either obtained from an outside source, or obtained from an assumed distribution

Uncertainty of Measurement Results

The combined standard uncertainty of the measurement result represents the estimated standard deviation of the result and is the positive square root of variance uc

2(y)

( )

The partial derivatives of f with respect to the Xi (referred to assensitivity coefficients) are equal to the partial derivatives of f with respect to the xi evaluated at Xi = xi; u(xi) is the standard uncertainty associated with the input estimate Xi; and u(xi, xj) is the estimated covariance associated with xi and xj.

Combining Uncertainty Components

uc2(y) =

i=1

N

∂xi

∂f∂xj

uc2(xi) ∂xi

2+ 2 Σ

i=1

N-1Σ

j=i+1

Nu(xi, xj)Σ ∂f ∂f

Expanded Uncertainty and Coverage Factor

a measure of uncertainty that defines an interval about theresult y within which the value of the measurand can be confidently asserted to lie is the expanded uncertainty, U, obtained by multiplying uc(y) by a coverage factor, k

Y = y ± UU = kuc(y)

k is typically 2 to 3- when U = 2 uc (i.e., k = 2), defines a level of confidence of approximately 95 %

- when U = 3 uc (i.e., k = 3) defines an interval having a level ofconfidence greater than 99 %

Propagation of Uncertainty

recoverypurity

measurementsand readings

confirmation

analyte speciationextractionefficiency

interference

homogeneity

test portionsize

uncertainty in the result

Uncertainty

the uncertainty on a resultwhich is traceable to a particularreference will be the uncertainty on that reference togetherwith the uncertainty on the measurement relative to thatreference

law of propagation of errors

EURACHEM / CITAC GUIDE CG4

Second Edition

QUAM:2000.1

Quantifying Uncertainty inAnalytical Measurement

Low uncertainty Fe isotope ratio measurements insea-water by ICP-MS at medium mass resolutionIvan Petrov and Christophe R. QuetelInstitute for Reference Materials and Measurements, JRC Geel, Belgium

uncertainty budget for measurement of an Fe isotope ratio

J. Anal. At. Spectrom., 2005, 20, 1095 - 1100

IUPAC isotopic composition

mass bias corrections

spiked sample ratio repeatability

68.4 %

21.4 %3.7 %

4.1 %

2.4 %

instrument background correctionfor sample

instrument background correctionfor mass bias

Cx = Cz

my

w mx

mz

m’y

Ay – By Rn

Bx Rn - Ax

Bz R’n - Az

Ay – By R’n- Cb

Practical aspects of the uncertainty and traceability of spectrochemical measurement results by electrothermal atomic absorption spectrometryS. Duta, P. Robouche, L. Barbu and P. TaylorInstitute for Reference Materials and Measurements, Geel, Belgium

Spectrochimica Acta part B 62 (2007) 337 - 343

tutorial on application of uncertainty calculations forestimation of U for determination of Cu in water using astandard calibration curve

and

concept of traceability through use of CRMs and certificates

Example of a Traceability Chain

references measurement processes u

Pb in serum RM, pure PbRM, mass, volume

validated method for Pb in serum, pure Pb RM

mass, volume

amount of Pb solution, mass

Pure Pb RM, mass

mass, current, atomicmass values, etc

SI

routine measurement of Pb in serum

IDMS of Pb in serum RM

reverse IDMS of Pb spike

prep of gravimetric solution of Pb

purity of Pb RM by coulometry

primary measurements of mass,current, at mass values, etc

Traceable Result

amount of Pb spike, mass

validation of routinemethod for Pb in serum

< 10-5

< 10-4

< 10-3

10-3

10-2

10-1

10-1

Accred Qual Assur (1997) 2: 354 - 359

Wolfgang Richter Primary Methods of measurement in chemical analysis

A method having the highest metrological qualities, whoseoperation can be completely described and understood,for which a complete uncertainty statement can be written down in terms of SI units, and whose results are, therefore,accepted without reference to a standard of the quantitybeing measured.

• gravimetry• titrimetry• coulometry• ID-MS• colligative properties• NAA

for a given quantity of X,the equation describing themeasurement method mustinclude no unknown function of X

the final link in a traceability chain is a primary direct method

Reference Material: material or substance, one or more of whose property values are sufficiently homogeneous and well establishedto be used for the calibration of an apparatus, the assessment of ameasurement method, or for assigning values to materials.

Dissemination of traceability: to deliver SI-traceable reference valuescarried by real-life samples to interested laboratories to enable them to determine the degree of equivalence of their own measurement result and a certified SI-traceable value

not every lab has access to primary methods…CRMs useful

Certified Reference Material: reference material, accompanied bya certificate, one or more of whose property values are certified bya procedure which establishes their traceability to an accurate realizationof the unit in which the property values are expressed, and for whicheach certified value is accompanied by an uncertainty at a stated level of confidence.

Some NRC-INMS Matrix CRMs

sampling sample prep weigh testportion

measurandextraction

removal ofinterferences

instrumental determination ofconcentration of measurand

resultvalue

efficiency ?losses ?

% recovery ?

efficiency ?losses ?

% recovery ?stability ofmeasurand ?

balance calibration

losses ?contamination ?

interferences - matrix effects ?

Matrix CRM(validation / traceability-IS)

Calibration CRM(traceability)

change state ofmeasurand

conversionefficiency ?

stability ofmeasurand

blank / spikes

Steps in a Typical Analytical Measurement Process

dry weight

Use of Certified Reference Materials CRMsPure substance (calibration ) CRMsMatrix (real sample - validation) CRMs

• instrument calibration• ensuring traceability

• method validation• statistical quality control (charting)• verification of operator training/performance

if the value of the CRM is part of the calculation of a result (i.e., a significantcorrection which is applied in the course of calculating the result), the result istraceable to that value;

if not, the CRM does not form part of the traceability chain but may be an important validation tool.

Are we there yet….?

“Well, this is just going from bad to worse.”

don’t worry….it’s more than half done….

public and privatesector labs required to

give evidence of their traceability

realization of SI units of measurementand their dissemination via CRMs

assist in dissemination of nationalmeasurement standards

chai

n o f

mea

s ure

men

tco

mp a

riso n

s

National Traceability Chain

INMETRO

CalibrationLaboratories

Routine MeasurementLaboratories

SIunits

diss

emin

atio

n

International Traceability Pyramids

co-ordinated by the 1999 MRA as well as…

NRCNIST

CENAM

MoU Between CIPM and ILAC

Laboratory Accreditation: ISO 17025

- link methodology to accreditation- reduce technical barriers to trade- strengthen existing MRAs- emphasis on technical competence

10,000 accredited laboratories41 country signatories

BIPM (MRA)

ILAC (MRA)

MoU

regional bodies accreditation

strong links between metrologyand accreditation

NMI links

2006

Standards Council of Canada (SCC)

• validation• traceability• uncertainty

(General Requirements for the Competence of Calibration and Testing Laboratories)

International Co-operation in Metrology

BIPM

NORAMET

EUROMET

APMPSIM

SADCMET

APLAC

SARAC

IAAC

EANACC

NMI collaborationRegional Metrology Organizations

laboratory accreditation

measurement capabilities are effectively linked globally….

IAAC = Inter-American Accreditation Cooperation

Signed in Paris in 1875by representatives of 17 nations. As well as founding the BIPM

currently 51Member States

the MRA(1999)

Metre ConventionMetre Convention

1875

General Conference on Weights and Measures( CGPM )

meets every four years and consistsof delegates from Member States

International Committee for Weights and Measures ( CIPM ) consists of eighteen individuals elected

by the CGPM It is charged with supervision of the BIPM

and affairs of the Metre Convention The CIPM meets annually at the BIPM

DiplomaticTreaty

Associate Statesand Economies

of the CGPM

Governmentsof

Member States

Internationalorganizations

Consultative Committees( CCs )

Ten CCs each chaired by a member of CIPM;to advise the CIPM; act on technical matters and

take important role in CIPM MRA; compriserepresentatives of NMIs and other experts.

Nationalmetrologyinstitutes( NMIs )

CIPMMRA

Bureau International des Poids et Mesures( BIPM )

International centre for metrology

Laboratories and offices at Sèvreswith an international staff of about seventy

The CIPM Consultative Committees

Consultative Committee on Metrology in each specificfield of metrology:

• Photometry and Radiometry – CCPR• Thermometry – CCT• Length – CCL• Time and Frequency – CCTF• Ionizing Radiation – CCRI• Mass and Related Quantities – CCM• Amount of Substance: metrology in chemistry – CCQM• Acoustics, Ultrasound and Vibration – CCAUV• Units - CCU

Metrologia, 1997, 34, 1-5

The Comite Consultatif pour la Quantite de Matiere:a brief review of its origins and present activitiesR. Kaarls and T.J. Quinn

• provide advice to the CIPM / BIPM• coordinate international intercomparisons• practical implementation of the CIPM MRA• regularly review technical needs and report to CIPM• fosters:

- comparability- traceability- accuracy- stated measurement uncertainty

CCQM Working Groups• Key Comparisons and CMC Quality• Organic Analysis• Inorganic Analysis• Gas Analysis• Electro-chemical Analysis• Surface Analysis• Bio-Analysis

Programme of work addressing the environmental area includes:• Heavy metals in water• Elemental speciation in sediment and bio tissues• Trace metals in sewage sludge (Cd, Cr, Cu, Hg, Ni, Pb, Zn)• Trace metals in foods and biotissues• Metals in fertilizer• Nitrite and nitrate in water•

150.00

155.00

160.00

165.00

170.00

175.00

180.00

185.00μ

mol

/kg

KCRV: 169.9 ± 1.6 mol/kgLGC

CSIR-NML

KRISSNRCCRM

NARL

NIST

NIMCNRC

IRMM

BAM

LNE

PTB

VNIIM

CENAM

μ

CCQM K-13Lead Content in Sediment

CCQM K43 Hg in Salmon Fish

LGC

0.310

0.330

0.350

0.370

0.390

0.410

0.430

0.450

:mol

/kg

KCRV: 0.3884 ± 0.0056 μmol/kg

KRISS NIST NRCIRMM NMIA LNENMIJ

80

82

84

86

88

90

NIST

PTBKRISS

LGCIR

MM

NRC

NMiNMIJ

LNEnm

ol /

kg

Cd: 83.49 ± 0.83 nmol/kg

CCQM - K-2 Key Comparison: Cadmium and Lead Contentin Natural WaterI. Papadakis, P.D.P. Taylor and P. De BiPvre

Metrologia 2001, 38, 543-547

449

499

549

599

649

BUD MAD NRCCRM USDA NMIA NRCC LGC PAU OVI NIST

Mas

s fr

actio

n of

SeM

et/ m

g kg

-1CCQM P86: Selenomethionine in Tablets

International Conformance Structure for Chemical Measurements

CCQM / RMOsOrganize Key ComparisonsCoordinate R&DManage MRA

NMIsPrimary measurement capabilityMeasurement standards

Reference LaboratoriesDevelopment & validation ofmethodsCRMsPT

Field LaboratoriesMeasurement validationQuality managementSample measurement

Valid measurements

Internationally trusted measurement results

ILAC / Regional OrganizationsEstablish criteria for AccreditationAccredit accreditation bodiesManage MRA

Accreditation bodiesAssessment of labs at all levels

Transparent evidence oftraceability and other qualityissues for the completemeasurement chain

peer review

peer review

peer review

Metrological Principles of Measurement

To achieve reliable measurements….

• trained and competent analysts• validated methods• procedures and tools for establishing traceability

- pure substance reference materials and calibration standards- matrix reference materials for validation

• procedures for determination of measurement uncertainty• quality control and proficiency testing• accreditation to an international standard (ISO 17025)

Conclusions

• the CIPM MRA, in conjunction with the BIPM / ILAC MoU,plays a major role in the globalization of efforts taken forassurance of comparable and traceable measurements.

“traceable to the SI” seeks to eliminate artifacts andanchor measurement results to inalterable properties of nature and in units derived from them

• the CIPM and the CCQM are engaged in meetingthis challenge

Will the Concept of Traceability be Accepted by Chemists ?

Planck’s principle“a new scientific truth does not triumph by convincing its opponentsand making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it”.

Metrology, the Science of Measurement....

• aims for global comparability of measurements and tests• traceable to the same long-term stable references• globally recognised and accepted measurement results

once measured/tested, everywhere accepted

Conclusions

“Well, I guess that ain’t a bad story -- but let me tell you about the time I lost this !“

and finally…

….for your kind attention

obrigado

Attributes of a (Chemical) Measurement

• ideally, measurement accuracy can be evaluated • every result derives from measurement of a ratio • results are expressed in multiples of a unit • every result carries an inherent uncertainty • measurement results should be universally commutable

(measured once, accepted everywhere )• results should be traceable to the agreed-upon unit• the SI system of units should be used when possible

(based on the constants of nature)

Accurate Precise

reference value

Measurement Results

Accuracycloseness of the agreementbetween the result of a measurement and a true value of the measurand

Uncertaintyparameter associated with the result of a measurement that characterizes thedispersion of the values thatcould reasonably beattributed to the measurand

International Vocabulary of Basic and General Terms in Metrology ISO 1993Guide to the Expression of Uncertainty in Measurement, ISO 1993

Traceability Scheme

Working Standard

routine method

Reference Standard

Primary Standard

primary method

SI

secondary method

responsibilityuncertainty

CGPM

CIPM, NMIs

accreditedcalibrationlabs

routine labs

traceability

NMIs: Providing Traceable Analytical Results

• certify traceable calibrations for standards, reference materials and PT scheme assigned values

• provide these calibrations and materials as services:– to field laboratories directly– to RM producers, PT scheme organisers, reference and

calibration laboratories

• work with regulatory and other official organisations

• ensure their services are reliable and form part of the International Measurement System:– adopt quality systems and third party accreditation or review– participate in the CIPM MRA

NRC Uncertainty Components for Hg in Salmon

reverse spike ratioR’n (39 %)

spiked sample ratioRn (60 %)

primary std concCz

dry mass correctionw

Cx = Cz

my

w mx

mz

m’y

Ay – By Rn

Bx Rn - Ax

Bz R’n - Az

Ay – By R’n- Cb

Model the input quantity in question by a probability distribution and estimate lower and upper limits a- and a+ to generate the best estimated value of the input quantity:• Normal probability distribution (± u encompasses about 68 % of the distribution)• Uniform (rectangular) distribution (± u encompasses about 58 % of the distribution)• Triangular distribution (± u encompasses about 65 % of the distribution)

Uncertainty of Measurement ResultsType B evaluation

µ = (a+ - a-)/2* √3 µ = (a+ - a-)/2* √6 µ = (a+ - a-)/2* √3

µtµtµt

µt is the expectation or mean of the distribution, and the shaded areas represent ± one standard uncertainty u about the mean.

Scheme for Key Comparisons

determination of purity

gravimetric preparation

precision measurement procedure

certification measurement procedure

routine measurement procedure

Traceability Chainsample solution wX(E)

Secondary standard YwY(E)industrial solution, Urel <0.3%

Transfer standard TwT(E)solution, Urel <0.1%

Primary standard Y

wY(E)solution S, Urel <0.05%

SINAkg and mol

pure substance, Urel <0.01% wpur

Sample X

Role of Traceability

Units come from standards

Csample = Cstd (Rsample / Rstd)

no traceability:

no unitsno uncertaintyno measurement

MRA Appendices at BIPM Website

• CIPM MRA signatories (Appendix A: 67 institutes)• Key and Supplementary comparisons (Appendix B)• Calibration and Measurement Capabilities (Appendix C: 25000)• list of Key Comparisons (Appendix D: 585 in database)

Primary Method Concept

Amount n(E) in sample X (e.g., mol)

R = n(E,X) / n(E,ES)

Amount n(E) in enriched spike (ES)

R = n(E,ES) / n(E,PS)

Amount n(E) in primary standard (PS)

SI unit (mass)

gravimetrym(PS) / m(kg)

[n(PS) / m(PS)] M(PS)

n(PS)amount to mass

stoichiometry

gravimetry

for a given quantity of E, the equation describing the measurementmethod must include no unknown function of E

gravimetry

gravimetry

trace

abili

ty

….for your kind attention

Thank you

Pinocchio in his later years

Suddenly, two bystanders stuck their heads inside the frame and ruined one of the funniest cartoons ever.