National Physical Laboratory of Israel

West Jerusalem, Israel

National Physical Laboratory of Israel

West Jerusalem, Israel

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Kuselman I.,National Physical Laboratory of Israel | Pennecchi F.,INRIM - Istituto Nazionale di Ricerca Metrologica | Burns C.,U.S. Food and Drug Administration | Fajgelj A.,International Atomic Energy Agency | de Zorzi P.,Instituto Superiore per la Protezione e la Ricerca Ambientale
Pure and Applied Chemistry | Year: 2012

A metrological background for investigating out-of-specification (OOS) test results of chemical composition is discussed. When an OOS test result is identified, it is important to determine its root causes and to avoid reoccurrence of such results. An investigation of the causes based on metrological concepts is proposed. It includes assessment of validation data of the measurement process and its metrological traceability chains, evaluation of measurement uncertainty, and related producer's and consumer's risks. This approach allows distinguishing between OOS test results that indicate an actual change in chemical composition of an analyzed object, and OOS test results that are metrologically related with a certain confidence probability, i.e., caused by measurement problems, while the analyzed object still meets the specification requirements at the time of testing. Practical examples illustrating applications of the described approach in environmental and food analysis, as well in drug analysis and stability study of drug products, are described. Acceptance limits, warning and action lines for the test results, and corresponding producer's and consumer's risks are discussed. © 2012 IUPAC.


Gadrich T.,ORT Braude College | Bashkansky E.,ORT Braude College | Kuselman I.,National Physical Laboratory of Israel
Accreditation and Quality Assurance | Year: 2013

Unbiased estimators of within-laboratory and between-laboratory (or within reference material unit and between-unit) variances of results of qualitative and semi-quantitative testing are formulated and discussed. Qualitative and semi-quantitative test results were treated as binary nominal and ordinal values, respectively, in framework of the newly developed ordinal analysis of variance (ORDANOVA). It is shown that the difference of the unbiased and the biased estimators of a within-laboratory variance does not exceed 5 %, when the number of replicate tests in a laboratory is larger than 20. Such a difference is increasing when the replicate number is decreasing, not depending on the number of laboratories and the between-laboratory variation, since both the unbiased and the biased estimators are based on the averaged within-laboratory variances. The difference of the unbiased and the biased estimators of the between-laboratory variance depends not only on the number of replicates, but also on the number of laboratories and on the ratio of the contributions to the total variance (the between-laboratory variance and the averaged within-laboratory variance). This difference does not exceed 5 %, when the number of replicates and the number of laboratories are larger than 20 and the ratio of the between-laboratory to the averaged within-laboratory variances does not yield 1. For a limited size of experiment (smaller numbers of replicates and laboratories), the difference is increasing with the size decreasing and can be significant. © 2012 Springer-Verlag Berlin Heidelberg.


Bashkansky E.,ORT Braude College | Gadrich T.,ORT Braude College | Kuselman I.,National Physical Laboratory of Israel
Accreditation and Quality Assurance | Year: 2012

Applications of a new statistical method Ordinal Analysis of Variance (ORDANOVA) for interlaboratory comparisons of measurement or test results of semi-quantitative (ordinal) and qualitative (binary) properties are discussed. ORDANOVA can be helpful for validation of measurement or test methods, proficiency testing of laboratories, development of reference materials with certified semi-quantitative and qualitative properties, that is, probably in every field where ANOVA is applied for quantitative properties. A statistics and criteria are proposed for performance assessment of laboratories active in semi-quantitative and qualitative testing and for other purposes of statistical analysis of such test results. © 2011 Springer-Verlag.


Kuselman I.,National Physical Laboratory of Israel | Fajgelj A.,International Atomic Energy Agency
Pure and Applied Chemistry | Year: 2010

A metrological background for implementation of proficiency testing (PT) schemes for a limited number of participating laboratories (fewer than 30) is discussed. Such schemes should be based on the use of certified reference materials (CRMs) with traceable property values to serve as PT items whose composition is unknown to the participants. It is shown that achieving quality of PT results in the framework of the concept "tested once, accepted everywhere" requires both metrological comparability and compatibility of these results. The possibility of assessing collective/group performance of PT participants by comparison of the PT consensus value (mean or median of the PT results) with the certified value of the test items is analyzed. Tabulated criteria for this assessment are proposed. Practical examples are described for illustration of the issues discussed. © 2010 IUPAC.


Tur'yan Y.I.,National Physical Laboratory of Israel
Reviews in Analytical Chemistry | Year: 2010

This review covers the theoretical bases of the analytical reaction between ammonium ion and formaldehyde for ammonium ion determination by formol titration. The nature of the product reaction, the product formation equilibrium constants, the product acid dissociation constants, the product yield, the reaction kinetics, and the optimum conditions for the reaction have been considered.


Kuselman I.,Independent Consultant on Metrology | Kuselman I.,National Physical Laboratory of Israel | Kuselman I.,National University of Science and Technology "MISIS" | Pennecchi F.,INRIM - Istituto Nazionale di Ricerca Metrologica
Pure and Applied Chemistry | Year: 2016

The classification, modeling, and quantification of human errors in routine chemical analysis are described. Classifications include commission errors (mistakes and violations) and omission errors (lapses and slips) in different scenarios at different steps of the chemical analysis. A Swiss cheese model is used to characterize error interaction with a laboratory quality system. The quantification of human errors in chemical analysis, based on expert judgments, i.e. on the expert(s) knowledge and experience, is applied. A Monte Carlo simulation of the expert judgments was used to determine the distributions of the error quantification scores (scores of likelihood and severity, and scores of effectiveness of a laboratory quality system against the errors). Residual risk of human error after the error reduction by the laboratory quality system and consequences of this risk for quality and measurement uncertainty of chemical analytical results are discussed. Examples are provided using expert judgments on human errors in pH measurement of groundwater, multi-residue analysis of pesticides in fruits and vegetables, and elemental analysis of geological samples by inductively coupled plasma mass spectrometry. © 2016 IUPAC & De Gruyter.


Gerasimenko E.O.,Kuban State University | Tur'yan Y.I.,National Physical Laboratory of Israel
Food Chemistry | Year: 2012

An automated flow pH-method for the determination of titratable acidity (TA) in edible oil without titration is proposed, based on pH measurements on an oil sample emulsion in a suitable reagent. The developed flow pH system involves two constant rate flows: the flow of oils samples and the flow of reagent: triethanolamine + KNO 3 + H 2O + i-PrOH, in which oils is insoluble. The flows are mixed in the mixer forming the emulsion in which the free fatty acids (FFA) extraction is started. Then, the emulsion is passed to the coil for completion of FFA extraction and thermostation and then forwarded to pH-cell for pH measurement. Using pH values and linear dependence of pH vs. log (TA) allows the TA determination. The optimum parameters for the automated flow pH-system have been found, i.e., volumes of the mixer and the coils, the rate of sample and reagent, pH and TA ranges. The results of the TA determination in the edible oils were statistically compared with the standard titration method. © 2011 Elsevier Ltd. All rights reserved.

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