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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.9, #7)

The 2nd International Conference on Metrology – Trends and Applications in Calibration and Testing Laboratories, 4–6 November 2003, Eilat, Israel by Ilya Kuselman (pp. 385-386).

Designs of experiment for proficiency testing with a limited number of participants by Ilya Kuselman; Marina Pavlichenko (pp. 387-390).

Metrological designs of experiment for proficiency testing (PT) with a limited number of participants are discussed. The designs are based on development of in-house reference materials (IHRMs) with traceable assigned values and “fit-for-purpose” uncertainties, used in a PT scheme as the measurement standards. When adequate certified reference materials (CRMs) are available, a comparative approach for IHRM development, using simultaneous analysis of IHRM and CRM test portions in pairs, is proposed for PT objectives. In the case where adequate CRMs are not available – for example, in the field of analysis of unstable aqueous systems – the function of the measurement standard for PT can be fulfilled by a synthetic IHRM prepared gravimetrically using non-adequate, non-aqueous CRMs or pure substances. The CRM or the pure substance is used as a spike for fortification of a natural water sample, while the natural water sample is used as a working IHRM for the spike determination. In this case the traceability chain is longer, since two IHRMs are added for one quantity determination, but it remains unbroken.

Keywords: Proficiency testing; Comparative approach; Reference materials; Traceability; Design of experiment

Sampling and metrology by Kaj Heydorn; Kim Esbensen (pp. 391-396).

The result of a measurement refers in principle only to the amount of substance actually contributing to the analytical signal. However, an appropriate definition of the measurand must include a specification of the system for which the result of the measurement should apply. All systems being inherently heterogeneous, representativity assumes importance for the metrological quality of a measurement, and the process needed to ascertain representativity is sampling. The contribution from this characteristic must be included when expressing the uncertainty of the reported value of the measurand. Representative sampling of systems that are infinite or non-uniform was developed by Pierre Gy in his Theory of Sampling. Finite systems can achieve uniformity by mechanical treatment and mixing; the heterogeneity of these systems can be characterized by a sampling constant, expressed in units of weight, for each particular species being determined. Examples of the contribution of sampling to the uncertainty of analytical results are discussed for some biological materials.

Keywords: Sampling constant; Uniformity; Heterogeneity; Sampling uncertainty

Current best practice for traceability in testing laboratories, when certified reference materials are unavailable by Tina Engelhard; Orna Dreazen (pp. 397-398).

Since the implementation of ISO/IEC 17025 in 2002, all accredited laboratories (at the least) need to establish traceability in all their tests and calibration methods. Traceabilty, though well understood in the calibration field (through an unbroken chain of comparisons to the International System of Units —SI), is less straight forward and not so well understood in the testing laboratories. Traceability in analytical and biological testing is found through the use of reference materials, and the validated steps of a test method. This article describes the possibilities to comply with the traceability requirement of ISO/IEC 17025 in testing laboratories , when certified reference materials are unavailable.

Keywords: Traceability; Reference materials; ISO/IEC 17025

Development of in-house reference materials for determination of inorganic polysulfides in water by Dan Rizkov; Ovadia Lev; Jenny Gun; Boris Anisimov; Ilya Kuselman (pp. 399-403).

In-house reference materials (IHRMs) for determination of inorganic polysulfides in water have been developed. The determination is based on the polysulfides’ derivatization with a methylation agent followed by GC/MS or HPLC analysis of the difunctionalized polysulfides. Therefore, the IHRMs are synthesized in the form of dimethylated polysulfides containing from four to eight atoms of sulfur. The composition of the compounds is confirmed by NMR and by the dependence of the HPLC retention time of the dimethyl polysulfides on the number of sulfur atoms in the molecule. Stability of the IHRMs is studied by HPLC with UV detection at 230 nm. Carbon tetrachloride solutions of the dimethyl polysulfides are stable at −20°C for 2 weeks, while their solutions in a mixture of acetonitrile and formic acid, 1:1, are stable even at +5°C for 3 weeks. The total sulfur content is controlled by the IHRMs’ oxidation with perchloric acid in high-pressure vessels (bombes) followed by determination of the formed sulfate using ICP-AES. Certified values of the dimethyl polysulfide concentrations are in the range of 416–3,327 ppm.

Keywords: In-house reference materials; Polysulfides; Synthesis; Separation; Stability; Characterization

Interlaboratory comparisons between results from testing metallurgical products for precious metal content by Yu A. Karpov; T. A. Makarova; D. F. Makarov; A. P. Kuznetsov (pp. 404-410).

Problems verifying the accuracy of analyses of non-standardized materials for precious metal (PM) content have arisen at the “Norilsky Nickel” plant, which is a major producer of nickel, copper, and PMs in Russia. Because of the unavailability of certified reference samples for direct accuracy verification, a program of interlaboratory comparisons (ILC) was developed. This program was based on testing three semi-products of the PM production process for PM content. On program completion, a total of 826 results in 98 runs had been obtained. For each run, the calculated mean value of PM concentration was taken to be the reference value. The results obtained by “Norilsky Nickel” were in agreement with the reference values within the standard deviations calculated for the values. The quality of results yielded with the ILC program, as assessed via the Z-criterion, is regarded as satisfactory.

Keywords: Interlaboratory comparisons; Precious metals; Analysis; Accuracy; Trueness

Metrology of polymorph identification tests by Berta Iosefzon-Kuyavskaya (pp. 411-414).

Identification of polymorphs – compounds containing the same chemical entities, but differing by their solid state properties – is a challenge for analytical chemists, since the solid state characteristics of polymorphs sometimes have subtle differences in their infrared (IR) spectra. A method based on the evaluation of FTIR spectra by Principal Component Analysis and a Software Independent Modelling Class Analogy package is proposed for estimation of reliability of polymorph identification. It is demonstrated that by proper choice of the spectral region, the same approach can be used for identification of polymorphs in low dosage formulations.

Keywords: Polymorph; Identification; FTIR; PCA

A priori method of evaluating uncertainties in qualitative chromatographic analysis: probabilistic approach by Vjacheslav Isaakovich Vershinin (pp. 415-418).

Probabilistic algorithms to evaluate result reliability in qualitative chromatographic analysis are discussed in the paper. The elementary uncertainty (P ₀), concerned with a single test (comparison of sample and reference peak positions), is treated as the sum of misidentification and omission probabilities. Both constituents are calculated separately using the simplified model and Laplace functions. In the model, the main reasons for elementary uncertainties are random normally distributed deviations during retention characteristic measurement. Algorithms to calculate both constituents of P ₀ have to take into account real measurement precision, supposed composition of the sample, content of the database, chosen coincidence criterion and other factors. At a high selectivity of retention, the 3σ value is recommended as the most convenient coincidence criterion. It leads to more reliable and unambiguous attribution of peaks in the chromatogram. For cases that are more complicated, the probabilistic algorithms based upon Bernoulli theorem are proposed to calculate the summary uncertainty of identification, concerned with the multiple test. They take into account P ₀ value, the number of repeated single tests (n) in the similar or different conditions, and chosen identification criterion K (minimal number of coincidences). The above-mentioned algorithms lead to a priori optimisation of the mode of operation of any identification software system associated with the chromatograph. They can be useful during a metrological validation of corresponding qualitative analysis methods.

Keywords: Qualitative chromatographic analysis; Identification; Repeatability; Retention characteristic; Probabilistic algorithms

Accreditation of sampling activities by Orna Dreazen (pp. 419-420).

Since the introduction of ISO/IEC 17025 it is a requirement for all accredited laboratories to include sampling in their quality statements. It is well understood that sampling and handling of the sample are key factors in the validity of a result. The fact that many laboratories worldwide are not involved in sampling poses a challenge to accreditors′ liability. This article describes the Israel Laboratory Accreditation Authority′s (ISRAC) and other accreditors′ approaches to sampling.

Keywords: Sampling; Validity; ISO/IEC 17025

Adequacy in the metrology of chemical analysis and other complicated measurements by V. I. Dvorkin (pp. 421-424).

The adequacy of specimens to each other, and of reference material to routine specimens, is an important idea in the metrology of chemical analysis. However, the literature gives no strict definition for this notion. In this paper, a determination of adequacy based on the measure of adequacy is proposed. For the case of two specimens, the measure of adequacy is the absolute value of the difference between the systematic errors in the results from analysis of the specimens; it depends on the differences in the composition and properties of the specimens. The measure of adequacy of a certified reference material to a population of routine specimens is the maximum distance between the systematic error of the reference material and one of the quantiles of the systematic error distribution of the routine specimens Q(0.025); Q(0.975); the errors in this case are due to the composition and the properties of the routine specimens and other complicated measurements. When the measure of adequacy can be neglected compared to the permissible error of the analysis, the specimens are considered adequate. Using the determination of total cholesterol in the blood serum of human beings as an example, it was shown that the certified reference material used in the analysis of specimens of complex composition is often inadequate when compared to routine specimens.

Keywords: Adequacy; Chemical analysis; Measurements; Certified reference material; Specimens

Reply to the letters to the editor by Samuel Wunderli, Accred Qual Assur (2003) 8:90 and 367 by Michael Thompson (pp. 425-426).

Accreditation of calibration laboratories to normative documents: diversity or standardization by Sergei Jacobson (pp. 427-428).

Calibration of measuring equipment is conducted by following some normative or applicable documents such as standards, manufacturer manuals and instructions, technical orders issued by defense organizations, or scientific papers. An accreditation body provides its recognition to the calibration laboratories by evaluating their technical competence and their compliance with the quality requirements of ISO/IEC 17025. The accreditation body must have defined criteria in order to evaluate different calibration methods which should ensure that the laboratories are performing the calibration in a technically competent manner when they are fully or even only partially based on the relevant reference documents. A discussion with different points of view about choosing the criteria, as well as the Israel Laboratory Accreditation Authority (ISRAC) policy on this issue, are presented.

Keywords: ISRAC policy on accreditation; Calibration laboratories; Normative documents

The impetus for and development of the National Analytical Measurement System (NAMS) by Yadong Yu; Jun Liu (pp. 429-433).

The National Analytical Measurement System (NAMS) underpins S&T innovation, economic and social development, and technical infrastructure for environmental protection and public health. It is a system that aids the economic growth of China. The purpose of NAMS is to effectively utilize analytical measurement resources to continually improve analytical measurement capabilities nationally, and to promote international comparability of measurement results. With the growth of economic globalization, China, wishing to promote economic links with countries around the world, needs to construct an effective NAMS which can contribute to the establishment of the global measurement system. By studying developed countries, drawing upon their experiences, and then considering the corresponding situation in China, this article proposes the establishment of a modern multi-level and multi-area virtual NAMS, which includes several analytical measurement resource databases, and a website platform providing technical services and technology dissemination. This article also describes the progress of “The Establishment and Improvement of NAMS of China” programme, supported by the central Chinese government, and implemented by a collaboration of more than 20 laboratories.

Keywords: Information database; Analytical methods; Reference materials; Network; National analytical measurement system

4th EURACHEM/CITAC/EQUALM International Workshop on Proficiency Testing in Analytical Chemistry, Microbiology and Laboratory Medicine, February 17–18, 2003, Bracknell, UK by Jean-Claude Libeer; Nick Boley; Brian Brookman (pp. 434-434).

European analytical column No. 32 (January 2004) by Miguel Valcárcel; Ernst-Heiner Korte (pp. 435-436).

7 / 2004 (pp. 437-438).

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.9, #7)

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.9, #7)