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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.8, #3-4)
Key conformity assessment players: OLAS – Luxembourg Office for Accreditation and Surveillance
(pp. b172-b172).
In search of the function of reference materials in the measurement process at CERMM-3, Rogasˇka Slatina, Slovenia
by P. De Bièvre (pp. 99-100).
”SoftCRM”: a new software for the Certification of Reference Materials by G. Bonas; M. Zervou; T. Papaeoannou; M. Lees (pp. 101-107).
A new software has been developed to be used for the storage and processing of the data in the frame of the development of new Certified Reference Materials (CRMs). This software includes separate Sections dealing with the main phases of the work necessary for the development of new CRMs, namely:The Homogeneity study, which includes the analysis of variance (ANOVA) of the sample set in case of equal (’balanced’) or unequal (’unbalanced’) number of replicates for each sample. The ANOVA Table is calculated and an F-test is performed to assess the significance of the ’between’ (i.e. ’among’) units and the ’within’ units standard deviations.The Stability study, which includes the linear regression of the data, the calculation of the slope and the assessment of its significance. In addition, the Standard Error of the Slope is calculated, to be used for the assessment of the uncertainty linked to the stability of the material.The Certification exercise, for the processing of the results obtained typically by different labs, which includes a set of tools (tests of the normality of the data set, tests for the detection of outlying means and variances, analysis of variance, etc) to assess the validity of the data and to calculate the property value. The possibility of electronic submission of the analytical data is provided to avoid possible errors during the transcription.The software is running under Windows in an interactive way and includes adequate outputs for each section, to be directly inserted in a Certification report or any other document. In addition, a Template for the editing of the Certification reports is included to facilitate and homogenize the reporting.
Keywords: Keywords Reference materials ; Homogeneity study ; Analysis of variance ; Stability study ; Certification
A need for clearer terminology and guidance in the role of reference materials in method development and validation by N. Majcen (pp. 108-112).
The fact that various definitions and terminology applied to measurements in analytical chemistry are not always consistent and straightforward, by not only answering the question ”what”, but also ”how”, leads to their various interpretations. This results in non-uniform implementation of very basic and essential metrological principles in chemistry. Such a diverse situation is not conducive to the endorsement of harmonised measurements all across the world, to serve as a tool for improving the quality of life in its broadest sense for all its citizens. The discussion in this paper is focused on problems associated with terminology and definitions of ’reference material’ and ’validation’. The role of reference materials in measurement processes for purposes other than calibration and validation principles in analytical chemistry are also discussed in this paper. Where possible, potential solutions are proposed, but more often, questions of essential importance are raised in order to initiate international discussion which will hopefully lead to equally understandable answers.
Keywords: Keywords Reference materials ; Analytical chemistry ; Measurements in chemistry ; Validation ; Method development
Preliminary study to prepare a reference material of styrene metabolites – mandelic acid and phenylglyoxylic acid – in human urine by I. Šperlingová; L. Dabrowská; V. Stránský; J. Kuˇcera; M. Tichý (pp. 113-116).
A preliminary batch of the reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. Tests for homogeneity and stability were performed by determining urine concentrations of mandelic (MA) and phenylglyoxylic acids (PGA). The urinary MA and PGA concentrations were followed over an 8-month period using high performance liquid chromatography (HPLC). No changes of the concentration values were found. Pure PA and PGA from Merck and Fluka, respectively, were used for traceability purposes, because certified or standard reference materials for MA and PGA do not exist. Control material ClinChek-Urine Control (Recipe) was analysed simultaneously. The mean values of MA and PGA compared well with the means of control samples and fell within the control range. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, homogeneity (277.0 ± 7.4 mg L−1 for MA and 148.0 ± 4.7 mg L−1 for FGA) and stability tests. The values are unweighted arithmetical averages of accepted results and their uncertainties are combined uncertainties enlarged by coefficient k=1, evaluated from the standard uncertainties of the interlaboratory comparison, homogeneity and stability tests.
Keywords: Keywords Reference material ; Styrene metabolites ; Uncertainty
Measurement uncertainty of selenium determination in the reference material Seronorm Trace Elements Serum by hydride generation atomic fluorescence spectrometry by D. Mazej; V. Stibilj (pp. 117-123).
An analytical result is not considered to be complete without a statement of the measurement uncertainty associated with it. Evaluation of measurement uncertainty is therefore an essential part of every determination. In the present study the measurement uncertainty of the result of determination of selenium in the reference material Seronorm Trace Elements Serum was studied. The combination of a digestion procedure using sulfuric acid, V2O5 in H2SO4 and hydrogen peroxide and the continuous flow approach of hydride generation atomic fluorescence spectrometry (HG-AFS) detection was used for selenium determination. The total uncertainty budget was calculated with the help of the GUM Workbench program, in which computations follow the rules of the ’ISO guide to the expression of uncertainty in measurement’. The major sources of uncertainty were found to be due to the recovery of the procedure, measurement of peak heights and the purity of Na2SeO3. A selenium mass fraction of 77.1±4.8 ng/g (with a coverage factor of 2.1, 95% probability) was determined, which is comparable with the recommended value of 80 ng/g.
Keywords: Keywords Measurement uncertainty ; Selenium ; Reference material ; Serum ; HG-AFS
New developments in the production and use of CRMs in Romania by M. Buzoianu (pp. 124-129).
A lot of effort is being made in Romania to meet the present main strategic goal – EU integration. Since the confidence in measurements is of considerable importance in almost every field of activity, the National Institute of Metrology (INM) is involved in improving its calibration and measurement capabilities to provide services in accordance with the latest European Regulation.Within this framework the assurance of the required traceability of all measurements plays a most important role. As reliable analytical measurements depend largely upon reference materials and the assurance of the traceability of amount measurements is still developing in Romania, a new approach regarding the function of Certified Reference Materials (CRMs) may be emphasized.The experience of the INM as well as new developments in Romania in preparation and certification of Reference Materials (RMs) are described. A short review of the locally available RMs and CRMs is given. Some aspects regarding the use of RMs and CRMs, especially for calibration, are discussed for their applicability for analytical measurements.
Keywords: Keywords Certified Reference Materials ; Calibration ; Analytical measurements
An estimation of the measurement uncertainty for an optical emission spectrometric method by T. Drglin (pp. 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.
Keywords: Keywords Optical emission spectrometer ; Steel ; Measurement uncertainty
Evaluation of measurement uncertainty in the determination of 210Pb and 210Po using beta counting and alpha spectrometry by P. Vreˇcek; L. Benedik (pp. 134-137).
Measurement uncertainties in the determination of 210Pb and 210Po in Reference Material IAEA-300 (Baltic Sea Sediment) were evaluated. 210Pb and 210Po were separated from the matrix using an Sr resin column. The chemical yield of 210Pb was determined gravimetrically in PbSO4 form. Precipitation was followed by beta proportional counting after 210Bi ingrowth. 210Po was determined by alpha spectrometry after its spontaneous deposition on a Cu planchet. The major source of uncertainty was identified as the statistical counting uncertainty, which was also expected and is almost impossible to reduce without extension of the time required for an analysis. The expanded uncertainties were determined as 7.4% and 12.2% for 210Pb and 210Po, respectively.
Keywords: Keywords Polonium ; Lead ; Measurement uncertainty ; Radioactivity
Uncertainty of chemical oxygen demand determination in wastewater samples by A. Drolc; M. Cotman; M. Roš (pp. 138-145).
The measurement uncertainty of the result of chemical oxygen demand determination in wastewater was evaluated. The major sources of uncertainty of the result of measurement were identified as the purity of reagents, volumetric operations, gravimetric operations, bias, and the repeatability of the method. Identification and evaluation of uncertainty sources was followed by combined uncertainty calculations. The combined uncertainty was compared to the experimentally determined variation and good agreement was found, indicating that the major uncertainty sources had been identified. The results show that the major sources of uncertainty arose from repeatability at high concentration level and volumetric steps at low concentration level, thus revealing the target operations for reducing the measurement uncertainty of this determination.
Keywords: Keywords Wastewater analysis ; Chemical oxygen demand ; Measurement uncertainty
Influence of sampling to the homogeneity of Cu-Ti-Zn alloy samples for the analyses with glow discharge optical emission spectroscopy by B. Kokliˇc; M. Veber (pp. 146-149).
Using Plackett-Burman experimental design the parameters of different ways of sampling (design and materials of the sampling mold, conditions of solidification of samples) that influence on the homogeneity of copper-titanium-zinc alloy samples in the production of titanium zinc were determined.Based on these results, the homogeneity of samples taken with two different sampling molds was investigated with GD-OES technique regarding alloyed elements (Cu and Ti) and impurities (Fe, Pb, Cd, Sn, Al) and was evaluated with analysis of variance (ANOVA).For Cu, Ti and Fe an overall (combined) uncertainty for different sampling approaches were estimated and compared to the expanded uncertainty evaluated without including the uncertainty due to sampling.
Keywords: Keywords Metrology in chemistry ; Uncertainty ; Homogeneity ; Sampling ; Titanium zinc
Interlaboratory comparisons – demonstrating degree of equivalence by R. Becker; I. Nehls; U. Dorgerloh (pp. 150-155).
The role of matrix reference materials in the process of demonstrating the degree of equivalence of measurement results obtained from intercomparisons is outlined, reviewing exemplary selected experience gained at BAM regarding the determination of organic contaminants in environmental matrices.The specific characteristics of reference materials employed in the process of demonstrating equivalence between laboratories in the course of proficiency testing as well as the development, comparison and validation of methods are elaborated. The demand is for series of appropriately characterised samples which are fit for the purpose and it is seen from representative examples that the utilisation of such tailor-made RM designed to tackle the specific need of an analytical problem dominates over certified matrix reference materials in this context. Concluding, the role of certified matrix reference materials in quality assurance is briefly looked at both from the user’s and providers’ points of view.
Keywords: Keywords Certification ; Equivalence ; Method development ; Proficiency testing ; Reference materials
An interlaboratory study to improve the quality of chemical and biological measurements in waste water by M. Cotman; A. Drolc; M. Roš (pp. 156-160).
Analyses of waste water are routinely performed to monitor the level of contamination. To verify the quality of such determinations the National Institute of Chemistry, with the support of the Ministry of Environment and Spatial Planning and the Slovenian Accreditation Agency, organizes interlaboratory comparisons. Over the last 3 years, five interlaboratory trials named "MPP-Waste Water" were organized. Each round attracted around 50 participants, mostly from Slovenia and some from abroad, which enabled the testing of SIST ISO methods or alternative methods. We prepared samples for determination of harmful substances that are important for the characterization of waste water; physico-chemical parameters (pH), global parameters – chemical oxygen demand (COD), biochemical oxygen demand (BOD5), metals (mercury, cadmium, copper, nickel, lead and chromium (VI)), nutrients (ammonia and total phosphorus), anions (chloride, nitrite, nitrate, sulphate) and toxicity to Daphnia magna. For the analysis of each parameter we prepared two samples at two different concentration levels. The materials used in the proficiency testing were carefully prepared and their homogeneity and stability were verified. The purpose of this scheme was to enable participants to check their day-to-day analytical performance. The results should enable the participants to improve the quality of their analyses.
Keywords: Keywords Proficiency testing ; Waste water ; Stability ; Homogeneity ; Reference value