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1.
Irina Ekeltchik Elena Kardash-Strochkova Orna Dreazen I. Kuselman 《Accreditation and quality assurance》2002,7(10):412-416
Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified
pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and
regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to
the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH
(e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the
required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with
experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and
with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard
reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties
of the experimental results are close to the predicted ones obtained by the simulation.
Received: 16 June 2002 Accepted: 19 July 2002
Presented at the 14th International Conference of the Israel Society for Quality, 18–21 November 2002, Jerusalem, Israel
Correspondence to I. Kuselman 相似文献
2.
Bertrand Lombard 《Accreditation and quality assurance》2006,11(1-2):94-100
Given the current interest in measurement uncertainty (MU) in food microbiology, in particular for laboratory accreditation
purposes, and the need to have harmonized reference documents specifically in that area at the international level, ISO is
conducting works to meet this need. An ISO Technical Specification (ISO/TS 19036) is being prepared on MU estimation for quantitative
determinations. A global approach has been chosen, based on the reproducibility standard deviation of the final result of
the measurement process. Three possibilities are envisaged for the estimation of the reproducibility standard deviation, in
a decreasing order of preference: The intra-laboratory standard deviation, the inter-laboratory standard deviation derived
from method validation, and the inter-laboratory standard deviation derived from proficiency testing.The uncertainty of qualitative
determinations is still under investigation, and will be covered by a separate ISO publication.
Presented at AOAC Europe/Eurachem Symposium March 2005, Brussels, Belgium 相似文献
3.
M. Buzoianu 《Accreditation and quality assurance》2000,5(6):231-237
In practice there are three aspects that need to be considered in order to achieve the required traceability according to
its definition: the 'stated reference', the 'unbroken chain of calibrations' and the "stated uncertainty". For a certain chemical
result, each of these aspects highly depends on the measurement uncertainty, both on its magnitude and how it was estimated.
Therefore, the paper describes the experience of the Romanian National Institute of Metrology in estimating measurement uncertainty
during the certification of reference materials (RMs), in metrological activities (calibration, pattern approval, periodical
verification, etc.), as well as during the analytical measurement process. Practical examples of estimation of measurement
uncertainty using RMs or certified reference materials are discussed for their applicability in spectrophotometric and turbidimetric
analysis. Use of the analysis of variance to obtain some additional information on the components of measurement uncertainty
and to identify the magnitude of individual random effects is described.
Received: 12 November 1999 / Accepted: 25 February 2000 相似文献
4.
T. Drglin 《Accreditation and quality assurance》2003,8(3-4):130-133
A validation procedure based on the ISO/IEC 17025 standard was used to demonstrate the long-term stability of a calibration
process and to assess the measurement uncertainty of a standard test method for optical emission vacuum spectrometric analysis
of carbon and low-alloy steel (ASTM E 415–99a). The validation was used to provide documented evidence that the selected method
fulfils the requirements and that the method is ”fit for purpose”. A test for drift was applied to determine statistically
whether the analytical results vary systematically with time. The accuracy and traceability of the optimised method were tested
by an analysis of closely matched matrix certified reference materials (CRMs). The measurement uncertainty estimations took
account of the precision study, the bias and its uncertainty, and the qualification of uncertainties not considered in the
overall performance studies.
Received: 2 November 2002 Accepted: 2 January 2003
Acknowledgement The author expresses gratitude to Dr. Aleš Fajgelj for helpful discussions during the 3rd Central European Conference on Reference Materials and Measurements.
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to T. Drglin 相似文献
5.
In the EURACHEM/CITAC draft ”Quantifying uncertainty in analytical measurement” estimations of measurement uncertainty in
analytical results for linear calibration are given. In this work these estimations are compared, i.e. the uncertainty deduced
from repeated observations of the sample vs. the uncertainty deduced from the standard residual deviation of the regression.
As a result of this study it is shown that an uncertainty estimation based on repeated observations can give more realistic
values if the condition of variance homogeneity is not correctly fulfilled in the calibration range. The complete calculation
of measurement uncertainty including assessment of trueness is represented by an example concerning the determination of zinc
in sediment samples using ICP-atomic emission spectrometry.
Received: 9 February 2002 Accepted: 17 April 2002 相似文献
6.
S. Küppers 《Accreditation and quality assurance》1997,2(1):30-35
Any analytical data is used to provide information about a sample. The "possible error" of the measurement can be of extreme
importance in order to have complete information. The measurement uncertainty concept is a way to achieve quantitative information
about this "possible error" using an estimation procedure. On the basis of the analytical result, the chemist makes a decision
on the next step of the development process. If the uncertainty is unknown, the information is not complete; therefore this
decision might be impossible. The major problem for the in-process control (IPC) procedure is that not only the repeatability
but also the intermediate precision (which expresses the variations within laboratories related to different days, different
analysts, different equipment, etc.) has to be good enough to make a decision. Unfortunately, the statistical information
achieved from one single analytical run only gives information about the repeatability. This paper shows that the estimation
of the measurement uncertainty for IPC is a way to solve the problem and gives the necessary information about the quality
of the procedure. An example demonstrates that an estimate of uncertainty based on the standard deviations of an analytical
method gives a value similar to one based on the standard deviations obtained from a control chart. Therefore, the estimation
is both a very useful and also a very cost-effective tool. Though measurement uncertainty cannot replace validation in general,
it is a viable alternative to validation for all methods that will never be used routinely.
Received: 24 May 1996 Accepted: 10 August 1996 相似文献
7.
A protocol has been developed illustrating the link between validation experiments, such as precision, trueness and ruggedness
testing, and measurement uncertainty evaluation. By planning validation experiments with uncertainty estimation in mind, uncertainty
budgets can be obtained from validation data with little additional effort. The main stages in the uncertainty estimation
process are described, and the use of trueness and ruggedness studies is discussed in detail. The practical application of
the protocol will be illustrated in Part 2, with reference to a method for the determination of three markers (CI solvent
red 24, quinizarin and CI solvent yellow 124) in fuel oil samples.
Received: 10 April 1999 / Accepted: 24 September 1999 相似文献
8.
Microbiological analyses are carried out on clinical, food, feed and environmental samples. The aims of the analyses are diagnostic
or estimation of the safety or the quality of the sample. Important decisions are made on the basis of microbiological analyses.
Little attention, however, is paid to the uncertainty of measurement of microbiological analyses. In microbiological cultivation
techniques the result is obtained by counting individual objects. The normally low number of counted objects strongly affects
the result of the analysis and its uncertainty. Because of the importance of the particle statistical variation to the uncertainty,
the approaches developed for chemical analyses are not directly applicable to microbiology. This paper discusses microbial
analyses and describes a novel guidance document for the estimation of measurement uncertainty in culturing methods [1].
Received: 7 October 2000 Accepted: 8 March 2001 相似文献
9.
A strategy is presented for applying existing data and planning necessary additional experiments for uncertainty estimation.
The strategy has two stages: identifying and structuring the input effects, followed by an explicit reconciliation stage to
assess the degree to which information available meets the requirement and thus identify factors requiring further study.
A graphical approach to identifying and structuring the input effects on a measurement result is presented. The methodology
promotes consistent identification of important effects, and permits effective application of prior data with minimal risk
of duplication or omission. The results of applying the methodology are discussed, with particular reference to the use of
planned recovery and precision studies.
Received: 28 October 1997 · Accepted: 17 November 1997 相似文献
10.
The new traceability system of measurement standards based on the Japanese Measurement Law has been established since November
1993. Some reference materials such as metal standard solutions, pH standard solutions and standard gas mixtures are included
in the system together with relevant physical quantities. In this system, primary measurement standard instruments or primary
reference materials are designated by the regulation for each quantity. For the practical dissemination of each quantity,
accreditation of calibration bodies is recognized by the steering committee under the supervision of the government. In the
course of assessment of a candidate calibration body, the concepts of ISO/IEC Guide 25 and ISO/IEC Guide 58 are effectively
introduced. For the estimation of reliability, the concept of how to introduce the statistical approach is effectively considered.
The method of uncertainty evaluation described in the ISO document entitled "Guide to the expression of uncertainty in measurement"
is adopted. 相似文献
11.
Dean A. Flinchbaugh L. F. Crawford David Bradley 《Accreditation and quality assurance》2001,6(12):493-500
A model is presented that correlates historical proficiency test data as the log of interlaboratory standard deviations versus
the log of analyte concentrations, independent of analyte (measurand) or matrix. Analytical chemistry laboratories can use
this model to set their internal measurement quality objectives and to apply the uncertainty budget process to assign the
maximum allowable variation in each major step in their bias-free measurement systems. Laboratories that are compliant with
this model are able to pass future proficiency tests and demonstrate competence to laboratory clients and ISO 17025 accreditation
bodies. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/
10.1007/s007690100398-y.
Received: 31 March 2001 Accepted: 11 September 2001 相似文献
12.
R. Kadis 《Accreditation and quality assurance》1998,3(6):237-241
Simple in principle, the evaluation of uncertainty, especially in chemical analysis, is not a routine task and needs great
care to be correct. This can be seen, particularly, from an examination of the EURACHEM Guide, Quantifying Uncertainty in Analytical Measurement (1995), which is the most important document on the subject. The examination reveals, in the author's opinion, a shortage
of correctness in some principal details of the uncertainty estimation process as presented in worked examples in the Guide,
and the author has therefore formulated some "in pursuit of correctness" rules for estimating uncertainty. The rules and respective
comments are concerned with the following items: (1) choosing an appropriate distribution function in type B evaluation of
uncertainty, (2) the necessity for consideration of separate contributions to the combined uncertainty, and (3) taking account
of actual influence factors in the uncertainty estimation process. Furthermore, the problem of estimation of conditional versus
overall uncertainty is touched upon in connection with comparative trials where only internal consistency of results is required.
Received: 29 January 1998 · Accepted: 10 February 1998 相似文献
13.
V. J. Barwick S. L. R. Ellison M. J. Q. Rafferty R. S. Gill 《Accreditation and quality assurance》2000,5(3):104-113
A protocol has been developed illustrating the link between validation experiments and measurement uncertainty evaluation.
The application of the protocol is illustrated with reference to a method for the determination of three markers (CI solvent
red 24, quinizarin and CI solvent yellow 124) in fuel oil samples. The method requires the extraction of the markers from
the sample matrix by solid phase extraction followed by quantification by high performance liquid chromatography (HPLC) with
diode array detection. The uncertainties for the determination of the markers were evaluated using data from precision and
trueness studies using representative sample matrices spiked at a range of concentrations, and from ruggedness studies of
the extraction and HPLC stages.
Received: 10 April 1999 · Accepted: 24 September 1999 相似文献
14.
S. L. R. Ellison 《Accreditation and quality assurance》1998,3(3):95-100
The possibility of using interlaboratory study repeatability and reproducibility estimates as the basis for measurement uncertainty
estimates is discussed. It is argued that collaborative trial reproducibility is an appropriate basis for estimating uncertainty
in routine testing provided certain conditions are met by the laboratory. The primary shortcomings relate to establishment
of traceability and consequent estimation of bias associated with the method, and quantitatively establishing the relevance
to the single laboratory. Approaches to resolving both difficulties are proposed, the former via full implementation of trueness
determination suggested in ISO 5725 : 1994 or by independent checks on individual accuracy and precision, the latter via a
reconciliation procedure. The paper also discusses other factors including sampling and sample pre-treatment, change in sample
matrix, and the influence of level of analyte.
Received: 28 October 1997 · Accepted: 17 November 1997 相似文献
15.
Stephan Küppers 《Accreditation and quality assurance》1997,2(7):338-341
The analytical chemists in process development in the pharmaceutical industry have to solve the difficult problem of producing
high quality methods for purity determination and assay within a short time without a clear definition of the substance to
be analyzed. Therefore the quality management is very difficult. The ideal situation would be that every method is validated
before use. This is not possible because this would delay the development process. A process-type quality development approach
with an estimation type fast validation (measurement uncertainty) is therefore suggested. The quality management process consists
of the estimation of measurement uncertainty for early project status. Statistical process control (SPC) is started directly
after measurement uncertainty estimation and a classical validation for the end of the project. By this approach a process
is defined that allows a fast and cost-efficient way of supporting the development process with the appropriate quality at
the end of the process and provides the transparency needed in the development process. The procedure presented tries to solve
the problem of the parallelism between the two development processes (chemical and analytical development) by speeding up
the analytical development process initially.
Received: 25 March 1997 · Accepted: 17 May 1997 相似文献
16.
17.
A procedure is presented for estimation of uncertainty in measurement of the pK(a) of a weak acid by potentiometric titration. The procedure is based on the ISO GUM. The core of the procedure is a mathematical model that involves 40 input parameters. A novel approach is used for taking into account the purity of the acid, the impurities are not treated as inert compounds only, their possible acidic dissociation is also taken into account. Application to an example of practical pK(a) determination is presented. Altogether 67 different sources of uncertainty are identified and quantified within the example. The relative importance of different uncertainty sources is discussed. The most important source of uncertainty (with the experimental set-up of the example) is the uncertainty of pH measurement followed by the accuracy of the burette and the uncertainty of weighing. The procedure gives uncertainty separately for each point of the titration curve. The uncertainty depends on the amount of titrant added, being lowest in the central part of the titration curve. The possibilities of reducing the uncertainty and interpreting the drift of the pK(a) values obtained from the same curve are discussed. 相似文献
18.
19.
M. Buzoianu 《Accreditation and quality assurance》1998,3(8):328-334
The need for reliability of measurements supporting legal decisions in environmental policy or medical diagnosis and treatment
is well known and widely accepted. This prerequisite can be met only by ensuring that legal measurements are accurate and
traceable to national or international standards. Consequently, an outline of the organizational structure of the Romanian
National Institute of Metrology (INM) for ensuring uniformity, consistency and accuracy of all measurements including legal
measurements performed in chemical laboratories is presented. Since reliable measurements can only be accomplished within
an appropriate traceability chain, the experience of the INM in identification and evaluation of measurement uncertainty in
legal activities concerning the environment and health is reviewed. Practical examples of measurement uncertainty evaluation
in spectrophotometric determination of five analytes, commonly determined in environmental and clinical chemistry are described.
The implications of measurement uncertainty for interpretation of regulatory compliance are discussed.
Received: 3 January 1998 · Accepted: 9 June 1998 相似文献
20.
M. Rösslein 《Accreditation and quality assurance》2000,5(3):88-94
This paper reviews the so-called "component by component approach" of evaluating measurement uncertainty. An overview of
the evaluation process is given followed by an in-depth discussion of some of the differences between this approach and the
approach of utilising validation data. Some of the advantages and disadvantages of using the component by component approach
are outlined at the end.
Received: 4 August 1999 · Accepted: 11 November 1999 相似文献