Slide1 : WHAT DOES INTERNATIONAL CHEMICAL COMMUNITY EXPECT FROM METROLOGY IN CHEMISTRY Aleš Fajgelj IAEA International Atomic Energy Agency Agency’s Laboratories Seibersdorf and Vienna Quality Assurance Supervisor IUPAC International Union of Pure and Applied Chemistry Interdivisional Working Party on Harmonization of Quality Assurance – Chairman Analytical Chemistry Division – Titular Member Workshop on:
METROLOGY IN CHEMISTRY
28 April 2005, Turin, Italy
International Atomic Energy Agency (IAEA) : International Atomic Energy Agency (IAEA) A. Fajgelj, April 2005, Slide 2 of 37 http://www.iaea.org
Slide3 : International Union of Pure and Applied Chemistry (IUPAC) Serves as a
Scientific
International
Non-governmental
Objective
Body in addressing the global issues involving the Chemical Sciences
In recognition of the role of chemistry as a central science in a wide range of fields, the term chemical sciences will be used to refer to chemistry, broadly defined, & to those scientific disciplines & technologies that make significant use of chemistry. http://www.iupac.org A. Fajgelj, April 2005, Slide 3 of 37
Slide4 : IUPAC’s Mission IUPAC's Mission is to advance the worldwide aspects of the chemical sciences and to contribute to the application of chemistry to the service of Mankind. In so doing, IUPAC will promote the norms, values, standards and ethics of science and advocate free exchange of scientific information and unimpeded access of scientists to participation in activities related to the chemical sciences. A. Fajgelj, April 2005, Slide 4 of 37
Slide5 : Objectives of the Union To promote continuing collaboration among the chemists of the member countries.
To study topics of international importance to pure and applied chemistry, which need standardization and codification.
To cooperate with other organizations which deal with topics of chemical nature.
To contribute to the advancement and understanding of pure and applied chemistry in all its aspects.
A. Fajgelj, April 2005, Slide 5 of 37
Slide6 : Too much!? WHAT DOES INTERNATIONAL CHEMICAL COMMUNITY EXPECT FROM METROLOGY IN CHEMISTRY? A. Fajgelj, April 2005, Slide 6 of 37
What is expected from / has to be done: : What is expected from / has to be done: field laboratories?
reference laboratories?
national metrological institutes?
related governmental bodies?
accreditation bodies?
reference material producers and suppliers of calibration (reference) sources, proficiency testing organizers?
on the international scene?
the users of analytical results (customers)?
educational institutions (faculties, high schools)?
A. Fajgelj, April 2005, Slide 7 of 37
Slide8 : International Standardization Scene Today 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2005 Paris AOAC
Int. Gaithersburg Geneva Vienna IAEA Geel IRMM Paris OECD NATA Sydney ILAC Frederick A2LA EUROLAB Berlin Barcelona EURACHEM Rio de Janeiro NIST IUPAC Research Triangle Park CITAC Rome FAO Delft EA BIPM ISO A. Fajgelj, April 2005, Slide 8 of 37
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Metrological traceability : Metrological traceability traceability: property of the result of a measurement or the value of a standard whereby it can be related to the stated reference, usually national or international standard, throughout an unbroken sequence of comparisons all having stated uncertainties. VIM 6.10 – ref: BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, International Vocabulary of Basic and General Terms in Metrology, 2nd edition, Geneva, 1993) comparability: to provide confidence that measurement results agree within the stated measurement uncertainty independent of: A. Fajgelj, April 2005, Slide 14 of 37
Some current problems & misunderstandings: : Some current problems & misunderstandings: Lack of understanding and definition of:
stated reference, traceability chain, calibrator Wrong perception that:
the unit of the SI is the only possible stated metrological reference
measurement result can be metrologically traceable to an institution
metrological traceability does not apply to the routine measurement results
the use of RMs for quality control purposes establishes metrological traceability
participation in proficiency tests or interlaboratory comparisons provides metrological traceability of measurement result Inconsistent terminology: VIM under revision (2003) A. Fajgelj, April 2005, Slide 15 of 37
Slide16 : International Union of Pure and Applied Chemistry Analytical Chemistry Division (V): Interdivisional Working Party on Harmonization of Quality Assurance Schemes Project:
INTERDISCIPLINARY HARMONIZED APPROACH TO METROLOGICAL TRACEABILITY OF CHEMICAL MEASUREMENT RESULTS www.iupac.org.projects/2001/2001-010-3-500.html www.iupac.org.projects/2003/2003-04-1-500.html A. Fajgelj, April 2005, Slide 16 of 37
Metrological Traceability : Metrological Traceability Stated reference
A. Fajgelj, April 2005, Slide 17 of 37
Use of calibration standards (calibrants) : Use of calibration standards (calibrants) Secondary calibrator Manufacturer’s product calibrator End user’s laboratory primary calibrator sample Manufacturer’s working calibrator Primary calibrator Working calibrator NMI End user’s laboratory sells to Reference material producer sells to A. Fajgelj, April 2005, Slide 18 of 37
Slide19 : (Questionable) Terminology related to CRMs A. Fajgelj, April 2005, Slide 19 of 37
Slide20 : Background At the first meeting of the CCQM an extended discussion takes place on the role and definition of primary methods and on reference materials in chemical measurements. Among the problems addressed is the question whether a realization of the mole is feasible and necessary. One of the results of the discussion are the following definitions:
Definition of a primary method of measurement:
A primary method of measurement is a method having the highest metrological qualities, whose operation 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 quantity being measured.
Definition of a primary reference material:
A primary reference material is one having the highest metrological qualities and whose value is determined by means of a primary method. The first meeting of the BIPM CCQM, April 1995, Sevres, France A. Fajgelj, April 2005, Slide 20 of 37
Slide21 : Background It is concluded that the following methods of measurement of amount of substance have the potential to be primary methods (as examples):
isotope dilution with mass spectrometry (IDMS);
coulometry;
gravimetry a) gas mixtures and b) gravimetric analysis];
titrimetry;
determination of freezing-point depression. Methods identified as having the potential to be primary: The application: Measurements of amount of substance, to be considered primary, must be made using a method which is specific for a defined substance and for which the values of all parameters, or corrections which depend on other species or the matrix, are known or can be calculated with appropriate uncertainty. Formation of working groups for each of identified method A. Fajgelj, April 2005, Slide 21 of 37
Slide22 : Background ..... after considerable discussion, the following revised definition was accepted:
Definition of a primary method of measurement:
A primary method of measurement is a method having the highest metrological qualities, whose operation can be completely described and understood, for which a complete uncertainty statement can be written down in terms of SI units
A primary direct method measures the value of an unknown without reference to a standard of the same quantity.
A primary ratio method measures the value of a ratio of an unknown to a standard of the same quantity; its operation must be completely described by a measurement equation. Amendment from the fourth meeting of the BIPM CCQM,
February 1998, Sevres, France A. Fajgelj, April 2005, Slide 22 of 37
Slide23 : Further information in the paper: This paper has been prepared for the CCQM as the basis for a document that summarises the answers to practical questions asked about primary methods. The authors propose that the document is updated regularly by the CCQM in order to help disseminate best practice in this area. Prepared by
Martin Milton, NPL, UK and Alain Marshal, BNM-LNE, France
for 6th CCQM Meeting, 23 February 2000 A. Fajgelj, April 2005, Slide 23 of 37
Slide24 : Measurement Relationships of analytical operations Test portion 2,3410 g Test solution Treated solution Aliquot Analytical data Chemical treatment Sampling A. Fajgelj, April 2005, Slide 24 of 37
Slide25 : Sampling site Sampling point Sampling unit Test area Increment/Primary sample Composite/aggregate sample Laboratory sample Test sample Drying, sieving, reducing, milling Sub-sample Analytical Operations Sampling pattern 1 2 3 ….n Relationships of sampling operations A. Fajgelj, April 2005, Slide 25 of 37
What is measurement uncertainty? : What is measurement uncertainty? “A parameter associated with the result of a measurement, that characterises the dispersion of the values that could reasonably be attributed to the measurand”. (VIM definition) X u “The uncertainty represents the range of values that the analyst believes could reasonably be attributed to the measurand.” “The uncertainty is a range in which we expect and claim our result to lay in with a certain confidence.” A. Fajgelj, April 2005, Slide 26 of 37
What is NOT a measurement uncertainty! : What is NOT a measurement uncertainty! It is not an error!
It is not traceability!
It is not just a statistical factor (parameter): a) from number of repeated of analysis
X ± sd (n = 6) b) from a laboratory intercomparison X ± sd (n = i) A. Fajgelj, April 2005, Slide 27 of 37
Slide28 : IC & traceability and uncertainty A. Fajgelj, April 2005, Slide 28 of 37
Slide29 : Reporting of results Measurement uncertainty is an integral part of the measurement result:
x U (k) A. Fajgelj, April 2005, Slide 29 of 37
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Slide31 : 1. Outlier examination
2. Fitting of repeatability standard deviation
as a function of concentration, ir(x)
3. Estimation of regression parameters
4. Estimation of matrix
5. Estimation of standard deviation of the estimation error at threshold value
6. Calculation of CC
7. Calculation of power function
8. Calculation of CC
9. Estimation of variance components
Measurements uncertainty A A. Fajgelj, April 2005, Slide 31 of 37
Slide32 : Quantity values and associates uncertainties assigned to properties of reference materials A. Fajgelj, April 2005, Slide 32 of 37
Slide33 : Recovery Quantitative analytical results should be corrected for recovery….
Recovery values should be established as a part of method validation
The method used for recovery estimation should be an integral part of the method protocol
IQC control charts for recovery should be established during method validation and used in all routine analysis In 1999 the IUPAC “Harmonized Guidelines for the Use of Recovery Information in Analytical Measurement” were published.
Pure & Appl. Chem., Vol 71, No. 2, pp 337-348, 1999
Technical principles of these guidelines were endorsed by IUPAC, AOAC. Int., EURACHEM, ISO REMCO:
A. Fajgelj, April 2005, Slide 33 of 37
Slide34 : Recovery and uncertainty When recovery (R) differs from 1 a correction is applied.
Since: ccorr = c/R ur must be included in the combined uncertainty
Combined uncertainty on the corrected result is included in the calculation: ucorr will be multiplied with coverage factor (k) to obtain the expanded uncertainty A. Fajgelj, April 2005, Slide 34 of 37
Slide35 : Measurement uncertainty and proficiency testing A. Fajgelj, April 2005, Slide 35 of 37
Slide36 : ISO/IEC 17025:1999 standard as a check list A. Fajgelj, April 2005, Slide 36 of 37
Major points of concern for chemical analytical laboratories : Major points of concern for chemical analytical laboratories ISO/IEC 17025:1999 standard requirements A. Fajgelj, April 2005, Slide 37 of 37