aspects regarding the present role and...

The First

International Proficiency Testing Conference

Sinaia, Romnia 11th 13th October, 2007

243

ASPECTS REGARDING THE PRESENT ROLE AND FUNCTION OF RMs AND CRMs IN CALIBRATION AND TESTING LABORATORIES

IN ROMANIA

Fnel Iacobescu1, Mirella Buzoianu21Romanian Bureau of Legal Metrology, Sos.Vitan Brzesti 11, 042122, Bucharest,

Romania, 2BRML - National Institute of Metrology, Sos.Vitan Brzesti 11, 042122, Bucharest,

Romania [email protected], [email protected]

Abstract The strong trend towards a free market of goods and services, the greater technical complexity of most products and services, increased concern with health, safety and environmental issues, and the growing emphasis on accreditation and international recognition of calibration and testing services require new demands toward the role and the function of reference materials (RMs) and certified reference materials (CRMs) in the measurement process in Romanian chemical laboratories. A broad representation of the principal metrological activities required at national level regarding RMs and CRMs is given. Also, the effort of the National Institute of Metrology (INM) towards updating the development and certification of CRMs of physical and chemical properties is presented. The interests and requirements of many users of RMs and CRMs are not limited to the regional scene as they are engaged in international trade, international co-manufacture of products and in QS implementation/accreditation. In the context of quality assurance, RMs are generally used for method validation, method development, internal quality control and external quality assessment purposes. Practical examples of how RMs and CRMs for chemical properties are used for method and instrument validation in Romanian testing and calibration laboratories are given. Some aspects concerning the use of environmental CRMs in assuring the accuracy of measurements, in evaluation of measurement uncertainty and in confirming the traceability of results, especially through calibration and validation, are discussed. Practical examples are given for each above-mentioned aspect. Also, the paper reviews the locally available environmental CRMs. The experience of the INM in certification of such materials issued in Romania is described. Since 2005, the INM started to implement and fulfill the requirements of the ISO Guide 34. The results obtained up to now are also discussed in the paper.

mailto:[email protected]

Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role and function of RMs and CRMs in calibration and testing laboratories in Romania

244

Key words Traceability, reference materials, certified reference materials, measurement uncertainty 1 INTRODUCTION Several European regulations related to the quality of ambient air/working spaces, of drinking water or food safety have been implemented lately within different legal issues. Most of them include requirements on the needed accuracy of measurement results, quantification limits or concentration ranges. To meet all these requirements, as well as the traceability and worldwide comparability of measurement results is a considerable challenge for the INM with its responsibility for ensuring the scientific background for the consistency and accuracy of all measurements in Romania. Present developments in this field are also related to the need to fulfil certain criteria for the mutual recognition of measurements. Therefore, INM concentrated on the improvement of a proper and traceable system of national and reference standards capable to assure the requested dissemination of any unit of measurement. Also, within the framework of a wide implementation and development of the quality infrastructure, at present the traceability is assured by the INM for all results, regardless of their accuracy or end-use. 2 REFERENCE STANDARDS AND MATERIALS DEVELOPED FOR PHYSICO-

CHEMICAL QUANTITIES Since its foundation on 1951, the INM developed a small group related to physico-chemical quantities. Following closely the needs for calibrations, pattern approvals and the periodic verifications of the analytical instruments, a laboratory, under different names, was responsible with physico-chemical quantities, such as: viscosity, density (of liquids), pH, concentration, humidity, etc. The present Physico-chemical Quantities Laboratory was set up in 2002, by merging three Groups on Reference Materials (build up in 1981), on Physico-chemical Quantities (build up in 1955) and on Gas Concentration (build up in 1978), respectively. Main methods of measurement developed by INM are presented in Table 1 and Reference Materials provided are summarized in Table 2.

Table 1 - Methods of measurement developed in the field

Physico-chemical quantity

Method of measurement

Measurement range

Expanded uncertainty (k =2)

Cinematic viscosity Flow due to gravity (0,03 ... 100) mm2s-2 (0,15 ... 0,50) % Density (of liquids) Hydrostatic weight (0,6 1,8) gcm-3 510-5 gcm-3

pH Comparative method (0 ... 14) 0,02 Mass fraction (in

liquid/ solid materials) Gravimetry

Spectro(photo)metry (0,001 ... 1,000) 2 % (rel)

Amount of substance concentration

Coulometry Titrimetry

(0,0001 ... 0,1000) molL-1

2 % (rel)

Humidity (in solids and gases)

Gravimetry / Two pressure standard

generated

(0 ... 100) 5 % (rel)

Volume fraction Gravimetric preparation of gas mixtures

(4010-6 ... 2010-2) (210-6 0,210-2)


245

Table 2 - Working RMs provided by the INM

RMs provided by the INM Measurement range Expanded uncertainty (k =2) Working standard solution for electrolytic conductivity

(40 5000) Scm-1 1 % (rel)

pH working standard solution (t = 20 C)

4.00; 6.88; 9.00 0,02

Spectrometric monoele-mental solutions

(0.500 ... 1.000) g kg-1

2 %

Synthetic sera (glucose, urea, calcium, magnesium

and creatinine

(

Gas mixtures working standards (CO, CO2, H2,

O2) in air or in N2

8810-6 910-2 210-6 0,110-2

Gas mixtures of hydro-carbons in air at the lower

limit of explosion (LIE)

3.110-3 3.710-2 3010-6 410-4

For the past five years several primary and reference methods of measurement were developed to better characterize reference materials and to improve the application of ISO Guide 35 [1]. Present development of measurement standards and reference materials for physico-chemical quantities was influenced by: - the implementation of a quality system in an increasing number of testing laboratories; more than 150 analytical laboratories working in environment protection field, water quality testing or clinical laboratories which have been accredited or are in the process of accreditation (several calibration services are required); - the increased awareness for accuracy, traceability and comparability of measurement results (due to the implementation of European regulations in the Romanian legislation); - the legal metrological control of the instruments and the measurements (a number of analytical instruments are subject to periodic verification). Therefore, the effort was concentrated to improve and develop the existing measurement standards as well to ensure the necessary reference materials required by the authorized metrological laboratories and/or calibration laboratories. 3 APPROACHES DEVELOPED FOR THE ESTIMATION OF MEASUREMENT

UNCERTAINTY RELATED TO CHEMICAL MEASUREMENTS The ISO Guide to the Expression of Uncertainty in Measurement [2] was adopted as national standard. Also, ENV 13005 has been adopted in 2005 as national standard. ISO GUM stands as the main reference for estimation and expression of measurement uncertainty at all levels of accuracy, from basic research and development to routine analysis. The growing interest for national and international comparability of all chemical measurement results, directed an increased attention for adequate application of this


246

document in standardization, calibration, laboratory accreditation, metrology services and routine chemical measurements. Statement of measurement uncertainty during calibration as well as after the validation of main performances of instruments underlined the need to consider measurement uncertainty in legal metrology. Determination of instrumental errors and comparison of these errors with maximum permissible limits are basic aspects considered in the necessary activities for legal metrology presented in [3] for spectro(photo)meteric measurements. According to the tasks of the INM in the field of chemical measurements, details of techniques used to estimate measurement uncertainty are given for the calibration of RMs spectrometric elemental solutions. Usually a spectrometric monoelemental solution is prepared according to a gravimetric procedure [4], involving metal/substance weighting; dissolution, solution weighting, bottling of the solution and mass fraction assessing. Accordingly, the schematic procedure used in the INM is described in figure 1.

National Mass standard

Weight High Purity elemental Form of chemical substances

Gravim etric method of preparation of m aterial

Preliminary fail Verification

pass

Preliminary evaluations (nominal value, trace level elem ents) to confirm the the gravimetrically content

Estimation of uncertainty of nominal value of mass conc. yes

Certification fail Possible criteria? Improvem ent

pass no

U :(0.015...0.020) RM certified RM c=1.000 g/L Calibration Certificate issued uncertified

Figure 1 - Schematic diagram for evaluation of measurement uncertainty associated with the mass fraction of elemental solution


247

Taking into consideration the measurement process, both evaluation of measurement uncertainty associated with the gravimetric procedure of preparation and assessment procedure applied in the INM are presented. 3.1 Measurement uncertainty associated with the mass fraction of elemental

solution

A summary of the evaluation of measurement uncertainty associated with the mass fraction of elemental solution assigned according to the gravimetric procedure is given in tables 3a and 3b.

Table 3a Evaluation of measurement uncertainty associated with the gravimetric procedure used within the INM measurement equation, procedures and main

sources of uncertainty

Measurement equations

metalsolutie

metal Pmm

= (1)

where: is the mass fraction of the metal present present in the gravimetrically prepared solution, mmetal is the real mass [g] of metal, msolutie is the real mass [g] of final solution, Pmetal is purity of the metal used. The Bouyancy correction is taken into account

Measurement procedures (as exemplified for copper spectrometric solution):

1. Metal surface cleaning; 2. Metal weighting; 3. Metal dissolution; 4. Final solution weighting; 5. Bottling the solution; 6. Mass fraction assessing.

Main sources of uncertainty

a) Gravimetric operations: uncertainty of the mass weights, bouancy, temperature, linearity of the balances, repeatability b) Metal purity

Table 3b Evaluation of measurement uncertainty associated with the gravimetric procedure used within the INM - Measurement uncertainty budget

Quantity Value Standard measu-rement uncertainty

Probability distribution

Relative measurement uncertainty

mmetal, g 0,216 60 0,000 08 normal 0,035 3 mfinal soln,

g 215,677 9 0,000 37 normal 0,000 2

Pmetal, unu

0,995 0,002 8 rectangular 0,290 1

Cu, mgg-1

0,999 3 0,0029 normal 0,292 5

Reported result: Cu (0,999 3 0,005 8) mgg-1

3.2 Measurement uncertainty associated with the mass fraction of elemental

solution assigned using EDTA procedure

A summary of the evaluation of measurement uncertainty associated with the mass fraction of elemental solution assigned according to the EDTA procedure is given in tables 4a and 4b.


248

Table 4a Evaluation of measurement uncertainty associated with the assay procedure used within the INM measurement equation, procedures and main

sources of uncertainty

Measurement equations

Meso

realEDTArationusedfortitEDTAMe MV

cV

=

ln

, (2)

where: Me is the mass concentration [g/L] of the metal present in the assesed mono-elemental solution; VEDTA used for titration is the real volume (corrected) [mL] of Na2-EDTA2H2O used for the titration; Vsoln is the real volume [mL] of mono-elemental solution taken for analysis; MMe is the molar mass of the metal [g/mol]; creal EDTA is the real amount of substance concentration [mol/L] of the Na2-EDTA2H2O used for the titration, evaluated against Zn standard

EDTAZn

ZnZnrealEDTA VM

Pmc

= 1000 (3)

where: mZn is the real mass [g] of Zn taken, determined using the Borda method and estimated against the indicated mass of the electronic balance, Bouyancy correction; PZn is Zn metal purity; MZn is Zn molar mass [g/mol]; VEDTA is the real volume of Na2-EDTA2H2O.

Measurement procedures:

1 Gravimetric preparation of Na2-EDTA2H2O soln. 0,05 mol/L; 2 Standardization of Na2-EDTA2H2O soln. 0,05 mol/L using Zn titrimetric standard traceable to NIST standard; 3 Measurement of the unknown concentration of the solution using the titrimetric method.

Main sources of uncertainty

a) Gravimetric operations: uncertainty of the mass weights, bouancy, temperature, linearity of the balances, repeatability b) Volumetric operations: volume calibration, temperature, repeatability, homogeneity of the titrant c) Stochiometry: purity and concentration of the titrant (Na2-EDTA2H2O), purity of all chemicals, molar masses, side reactions d) The bias of the equivalence point: measured equivalence = stochiometric equivalence e) Metallic purity of the starting materials

Table 4b Evaluation of measurement uncertainty associated with the assay procedure used within the INM - Measurement uncertainty budget

Quantity Value Standard measurement

uncertainty

Probability distribution

Relative measurement

uncertainty srepeatability 1) 1 0.001/3= normal 0.000 577 mZn, [g] 0.080 50 0,000 03 normal 0.000 372 6 PZn 1.000 1 0.000 288 6 rectangular 0.000 288 6 BBZn 1.000 018 0.000 01 rectangular 0.000 01 MZn, [g/mol] 65.39 0.02 rectangular 0.000 31


249

VEDTA, [mL] 2) 2.468 0.001 8 triangular 0.000 742 creal EDTA [mol/L]

0.049 88 0.000 05 normal 0.001 096

srepeatability1) 1 0.003/3 normal 0.001732 VEDTA used for titration [mL] 3)

7.882 0.033 triangular 0.004186

creal EDTA, [mol/L]

0.049 88 0.00005 normal 0.001096

VCu soln, [mL] 25.00 0.015 triangular 0.0006 MCu, [g/mol] 63.546 0.003 rectangular 0.0000472 PDA 0.99 0.01/3 rectangular 0.0057 Cu, [g/L] 0.9993 normal 0.00738 Reported result: Cu (0,999 0,015) g/L (20 C) for k=2 and PP*=95 %

Notes: 1) Usually, three parallel measurements are done 2) The value is a corrected one for the calibration factor and bias due to the detection of the equivalence point. The influences of calibration, temperature effect (a maximum difference of T=3 C from the nominal value of 20 C is accepted according to the internal Procedure PS-01-05-01-INM) and the bias of the detection of the equivalence point (max. of 0.3 %) were considered. The bias was evaluated against ICP Zn Certipur Reference Material 3) The value was corrected with a calibration factor and the bias due to the detection of the equivalence point. The uncertainty associated with the volume of the EDTA included also the uncertainty of the correction factor for the detection of the equivalence point (maximum of 0.3 %) and the selectivity of the method. The correction factor for the detection of the equivalence point was evaluated against ICP Cu Certipur Reference Material. 3.3 Confirmation of the measurement capabilities

Knowledge of the comparability of SI standards realized and maintained at the national level is an important factor in creating worldwide confidence in the abilities and capabilities of national metrology institutes (NMIs). In 1999, the International Committee of Weights and Measures (CIPM) therefore drew up a Mutual Recognition Arrangement (CIPM MRA). This provides the basis for the acceptance, by NMIs, and other signatories, of calibration and test certificates from other NMIs. The CIPM MRA provides users with transparent, comprehensive, reliable, peer reviewed, quantitative information on the capabilities of NMIs and the degree of equivalence of the SI units and quantities they maintain. It provides the technical framework for several agreements negotiated for international trade, commerce and regulatory affairs in those cases where acceptance and equivalence of the results of measurements are important. Under the CIPM MRA, signatories initially state what they claim to be the measurement uncertainty of the services they provide. These so-called Calibration and Measurement Capabilities (CMCs) are, broadly speaking, the uncertainties they attribute to their calibration and test services. Confidence in the CMCs is underpinned firstly by the participation in a number of key comparisons which test the principal techniques in that field, and secondly by a detailed examination of the CMC claims by technical peers drawn from the RMOs worldwide. These claims are then finally


250

analyzed by the JCRB (Joint Committee of the Regional Organizations and the BIPM). The results of key comparisons are published and are also available on the BIPM website (www.bipm.org), as is a database of these results and the CMCs which have been accepted by the world community. Within this framework, the INM confirmed the measurement capability both in the case of gravimetric procedure of preparation of spectrometric solutions and in the case of calibration of such solutions by participating in the CCQM P46 [5] and EUROMET 763 projects [6]. The obtained results are illustrated in figure 2 (CCQM P46) and in figure 3 (EUROMET 763).

0.96

0.965

0.97

0.975

0.98

0.985

0.99

0.995

1

1.005

1.01

BAM

LGC

NRC

INM

KRISS

CENA

MNM

IJSM

UNI

ST UME

PTB

Laboratory

Rel

ativ

e S

D ift

Figure 2 - Results of mass fraction of copper in spectrometric solution measured at the NIST, USA

0,9678

0,9825

0,9972

1,0119

g/kg

0.6990

0.6900

UME LNE INM SPI

0,0

Relative deviation, %

- 1,5

+ 1,5

- 2,9

+ 2,9

Figure 3 - Results of copper (nominal mass fraction of 1 gkg-1) comparison


251

Accordingly, the calibration and measurement capability in this field is published at present in the BIPM database [7]. 4 PRESENT AND PERSPECTIVES OF METROLOGY IN CHEMISTRY Main metrology concepts needed to be applied to chemical measurements carried out at field laboratories refer to: 1. Validation of the methods of measurement used; 2. Measurement uncertainty associated with the reported analytical result; 3. Traceability of measurement results to internationally recognised references

(preferably to SI) via internationally recognised measurement standards; 4. Calibration and measurement capabilities demonstrated in MRA relevant

comparisons. At present the INM carries out a limited range of experimental activity concentrated on those measurements most needed in the country. In this respect, main intended future actions [8] concentrate on: - Realisation of primary measurement standards at least for cinematic viscosity, mass concentration and density (for liquids); - Development of reference materials able to ensure the means to achieve the traceability from calibration laboratories to field laboratories; - Development of new primary methods of measurement (there is a research program currently going on aimed at developing coulometry); - Participation in key comparisons to demonstrate the equivalence of national measurement standards; - Extending the ISO Guide 34 implementation from Cu elemental solution to pH and electrolytic conductivity RMs issued by the INM. A large part of the resources is invested in expanding the collaboration with reference laboratories in order to set up a network of laboratories able to assure o sound support in a specific chemical measurement. Also knowledge transfer by participating in teaching/training courses on traceability, uncertainty, validation etc. 5 CONCLUSIONS The paper depicted main reference materials and measurement standards developed by the INM in order to assure the traceability of all measurement results reported in chemical determinations. CMCs approved in metrology in chemistry were described. Main activities identified to assure and demonstrate the traceability of physico-chemical results and the values of the specific measurement standards are: - attestation of new national measurement standards especially those standards having

demonstrated the measurement capability during different relevant comparisons; - diversification and development of the existing reference materials in order to

enable them to meet all the requirements of the industry and commerce; - proactive participation of the INM in MRA comparisons.


252

REFERENCES [1] ISO Guide 35:2006 Reference Materials General and statistical principles for

certification [2] Guide to the Expression of Uncertainty in Measurement, ISO (1995) Geneva [3] Buzoianu M.: Measurement Uncertainty and Legal Limits, Bull. OIML [4] Kipphardt H., Matschat R., Rienitz O., Schiel D.: Traceability system for

elemental analysis, Accred. Qual. Assur. 10, 633639, (2006) [5] Turk, G.C.; Winchester, M.R.; Butler T.A.: CCQM-P46 on the Preparation of

Elemental Solutions, Progress Report, (2004) [6] EUROMET 763 Final Report, www.euromet.org [7] BIPM database, www.bipm.fr [8] Iacobescu F.; Popescu I.M.; Buzoianu M.: New National and Reference

Standards Developed In the Field of Physico-Chemical Measurements In Romania, Proceedings of the International Congress of Metrology, France, (2004)

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34_Duta-MT_P0128.doc35_Iacobescu-Buzoianu_MT_O_P0121.doc1 INTRODUCTION2 REFERENCE STANDARDS AND MATERIALS DEVELOPED FOR PHYSICO-CHEMICAL QUANTITIES3 APPROACHES DEVELOPED FOR THE ESTIMATION OF MEASUREMENT UNCERTAINTY RELATED TO CHEMICAL MEASUREMENTS3.1 Measurement uncertainty associated with the mass fraction of elemental solution3.2 Measurement uncertainty associated with the mass fraction of elemental solution assigned using EDTA procedure3.3 Confirmation of the measurement capabilities

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37_Muntean_MT_P_P0086.rtf1 INTRODUCERE2 TRASABILITATEA N SISTEMUL DE COLECTARE A LAPTELUI3 ANALIZE PENTRU CONTROLUL CALITII4 CONCLUZIIREFERENCES

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39_Koncsag_VTM_O_P0054_grigore.doc1 INTRODUCTIONThe determination of heavy metal content in the sludge is a matter of environment and a concern for managers since the environment legislation hardens. In order to have a right evaluation of the risk at the disposal of this waste, it is important to have a valid method for its characterization.2 EXPERIMENTAL2.1 Materials and equipment2.2 ProceduresTechniqueDigestorDigestion typeSample quantityA1. Graphite oven B1. MicrowavesC1. HNO3D1. 1gA4. ICP-AES-C4. H2SO4+HCl---C5. HNO3+HCl+ H2O2---C6. HNO3+HCl+HF-

3 RESULTS AND DISCUSSIONS4 CONCLUSIONSREFERENCES***STAS 13094/ mai 1992 Nmoluri rezultate de la tratarea apelor de suprafa i epurarea apelor uzate. Determinarea coninutului de nichel.

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aspects regarding the present role and...

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