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ASPECTS REGARDING THE PRESENT ROLE AND FUNCTION OF RMs AND CRMs IN
CALIBRATION AND TESTING LABORATORIES
IN ROMANIA
1Romanian Bureau of Legal Metrology, Sos.Vitan Bârzesti 11, 042122,
Bucharest, Romania,
2BRML - National Institute of Metrology, Sos.Vitan Bârzesti 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.
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
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)
g⋅cm-3 5⋅10-5 g⋅cm-3
pH Comparative method (0 ... 14) 0,02 Mass fraction (in
liquid/ solid materials) Gravimetry
Amount of substance concentration
Gravimetry / Two pressure standard
(40⋅10-6 ... 20⋅10-2) (2⋅10-6 … 0,2⋅10-2)
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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) μS⋅cm-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
and creatinine
O2) in air or in N2
88⋅10-6 … 9⋅10-2 2⋅10-6 … 0,1⋅10-2
Gas mixtures of hydro- carbons in air at the lower
limit of explosion (LIE)
3.1⋅10-3 … 3.7⋅10-2 30⋅10-6 … 4⋅10-4
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
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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
Preliminary fail Verification
pass
Preliminary evaluations (nominal value, trace level elem ents) to
confirm the the gravimetrically content
Estimation of uncer- tainty 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
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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
⋅=ω (1)
where: ω 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
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
Pmetal, unu
ωCu, mg⋅g-1
Reported result: ω Cu (0,999 3 ± 0,005 8) mg⋅g-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.
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
248
Table 4a – Evaluation of measurement uncertainty associated with
the assay procedure used within the INM – measurement equation,
procedures and main
sources of uncertainty
,ρ (2)
where: ρMe 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
⋅= 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
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
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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
srepeatability 1) 1 0.003/√3 normal 0.001732
VEDTA used for
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
ρCu, [g/L] 0.9993 normal 0.00738 Reported result: ρCu (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 ΔT=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
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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
R el
at iv
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
- 1,5
+ 1,5
- 2,9
+ 2,9
Figure 3 - Results of copper (nominal mass fraction of 1 g⋅kg-1)
comparison
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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.
Fnel Iacobescu, Mirella Buzoianu Aspects regarding the present role
and function of RMs and CRMs in calibration and testing
laboratories in Romania
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, 633–639, (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)
31_Albeanu_UM_P_P0102.doc
2.3 Simultaneous confidence bands
3 EXPERIMENTAL RESULTS
5 CONCLUSION
2.2 Standardization
2.3 Calculation
3.1 urel(c)——uncertainty caused by preparation of EDTA standard
solution
3.2 urel(k)——sub-quantity of uncertainty caused by standard
coefficient k
3.3 urel (L)——sub-quantity of uncertainty caused by transferring
proportion
3.4 u(V)——sub-quantity of uncertainty caused by EDTA standard
solution added in excess
3.5 urel(V)——sub-quantity of uncertainty caused by Zn standard
solution during titration sample solution titrate with Zn standard
solution, the maximum tolerance error of 50mL burette is (0.05mLthe
volume of consumed Zn standard solution V is 38.12 mLso
4 Discussion
2 REFERENCE STANDARDS AND MATERIALS DEVELOPED FOR PHYSICO-CHEMICAL
QUANTITIES
3 APPROACHES DEVELOPED FOR THE ESTIMATION OF MEASUREMENT
UNCERTAINTY RELATED TO CHEMICAL MEASUREMENTS
3.1 Measurement uncertainty associated with the mass fraction of
elemental solution
3.2 Measurement uncertainty associated with the mass fraction of
elemental solution assigned using EDTA procedure
3.3 Confirmation of the measurement capabilities
4 PRESENT AND PERSPECTIVES OF METROLOGY IN CHEMISTRY
5 CONCLUSIONS
2.1 The 4πPC-γ coincidence method
2.2 The Liquid Scintillation - Triple to Double Coincidence Ratio
method (LSC-TDCR)
3 INTERNATIONAL EQUIVALENCE
3.1 Key comparisons
3.1.2 Comparisons codified as: “BIPM.RI(II)-K1.Radionuclide”
3.1.3 Comparisons codified as: “EUROMET .RI(II)-K2.
Radionuclide
3.2 Supplementary comparisons included in KCDB
3.3 Regional and bilateral comparisons
3.4 Elaboration of the Calibration and Measurement (CMC)
documents
4 NATIONAL TRACEABILITY
3 ANALIZE PENTRU CONTROLUL CALITII
4 CONCLUZII
3 DESIGN OF THE COLLABORATIVE STUDY
3.1 General Principles
3.2 Participating Laboratories
3.3 Test Materials
1 INTRODUCTION
The 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 EXPERIMENTAL
REFERENCES
***STAS 13094/ mai 1992 – Nmoluri rezultate de la tratarea apelor
de suprafa i epurarea apelor uzate. Determinarea coninutului de
nichel.
40_Vaquero_VTM_P_P0080.doc
2.1 Comparative study of the matrix of some different filters
2.2 Homogeneity of the filters
3 FINAL DISCUSSION