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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #10)
Interpretation of interlaboratory comparison results to evaluate laboratory proficiency by Rob G. Visser (pp. 521-526).
Guidelines are given for the evaluation of proficiency test (PT) results in order to increase the effectivity of PT participation. For better understanding, some statistical background is given along with some examples to show the effects of the choices made by the PT provider. The calculation method of the assigned value and the selection of the standard deviation both affect the z-score that is used by the participating laboratory to judge the quality of its performance in the PT. Therefore, the participating laboratory is advised to use the PT results with care and, if necessary, to recalculate the z-scores. Finally, advice is given on how not to follow up bad PT results along with some valuable steps that could be part of an effective follow-up procedure.
Keywords: Proficiency test; Assigned value; Standard deviation; z-score; Root cause analysis; Corrective action; Effectivity
Interpretation of interlaboratory comparison results to evaluate laboratory proficiency by Rob G. Visser (pp. 521-526).
Guidelines are given for the evaluation of proficiency test (PT) results in order to increase the effectivity of PT participation. For better understanding, some statistical background is given along with some examples to show the effects of the choices made by the PT provider. The calculation method of the assigned value and the selection of the standard deviation both affect the z-score that is used by the participating laboratory to judge the quality of its performance in the PT. Therefore, the participating laboratory is advised to use the PT results with care and, if necessary, to recalculate the z-scores. Finally, advice is given on how not to follow up bad PT results along with some valuable steps that could be part of an effective follow-up procedure.
Keywords: Proficiency test; Assigned value; Standard deviation; z-score; Root cause analysis; Corrective action; Effectivity
Visualization technique for uncertainty budgets: Onion charts by Kenneth W. Pratt; David L. Duewer (pp. 527-530).
A concise graphical depiction, the “onion” chart, is described for presenting uncertainty budgets for any measurand, y, having a set of component variances, $$u_i^2 (y)$$ . The onion chart consists of a concentric series of rings. Each ring is constructed from the set of fractional contributions, $$u_i^2 (y), / sum {u_i^2 (y)}$$ . The outer ring includes all $$u_i^2 (y)$$ and depicts the combined standard uncertainty, u c (y), where u c 2(y) ≡ ∑u i 2(y). Moving inward, each successive ring deletes the largest remaining $$u_i^2 (y)$$ . A “reduced” $$sum {u_i^2 (y)}$$ is calculated for that ring from the remaining set of $$u_i^2 (y)$$ , with the fractional contributions calculated using the “reduced” $$sum {u_i^2 (y)}$$ . This format facilitates rapid visual comparison of the importance of each component, with minor components becoming visible as the larger components are successively deleted. An example is presented using data from pH metrology, including the physical interpretation of the resulting diagram.
Keywords: Graphical tool; Onion chart; pH metrology; Pie chart; Uncertainty analysis
Visualization technique for uncertainty budgets: Onion charts by Kenneth W. Pratt; David L. Duewer (pp. 527-530).
A concise graphical depiction, the “onion” chart, is described for presenting uncertainty budgets for any measurand, y, having a set of component variances, $$u_i^2 (y)$$ . The onion chart consists of a concentric series of rings. Each ring is constructed from the set of fractional contributions, $$u_i^2 (y), / sum {u_i^2 (y)}$$ . The outer ring includes all $$u_i^2 (y)$$ and depicts the combined standard uncertainty, u c (y), where u c 2(y) ≡ ∑u i 2(y). Moving inward, each successive ring deletes the largest remaining $$u_i^2 (y)$$ . A “reduced” $$sum {u_i^2 (y)}$$ is calculated for that ring from the remaining set of $$u_i^2 (y)$$ , with the fractional contributions calculated using the “reduced” $$sum {u_i^2 (y)}$$ . This format facilitates rapid visual comparison of the importance of each component, with minor components becoming visible as the larger components are successively deleted. An example is presented using data from pH metrology, including the physical interpretation of the resulting diagram.
Keywords: Graphical tool; Onion chart; pH metrology; Pie chart; Uncertainty analysis
Accreditation of GMO detection laboratories: Improving the reliability of GMO detection by Jana Žel; Katarina Cankar; Maja Ravnikar; Marjana Camloh; Kristina Gruden (pp. 531-536).
Reliable and efficient methods for detecting genetically modified organisms (GMOs) are essential for establishing an effective system for traceability all along the supply chain from seed producers to final consumers. The latter is especially meaningful in European Union and other countries where strict legislations on GMOs were set up. Performance of the methods used in laboratories around the world should be uniform, in order to obtain reliable and comparable results. Accreditation is a suitable system for harmonising procedures in each testing laboratory. In this paper, key elements for the accreditation of molecular biology methods for GMO detection according to ISO/IEC 17025 are described. The procedures described are also valuable for the accreditation of molecular methods for all laboratory diagnostics where qualitative and quantitative characterisation of nucleic acids is needed.
Keywords: Accreditation; Genetically modified organisms; Molecular methods; Quantitative PCR; Quality assurance
Accreditation of GMO detection laboratories: Improving the reliability of GMO detection by Jana Žel; Katarina Cankar; Maja Ravnikar; Marjana Camloh; Kristina Gruden (pp. 531-536).
Reliable and efficient methods for detecting genetically modified organisms (GMOs) are essential for establishing an effective system for traceability all along the supply chain from seed producers to final consumers. The latter is especially meaningful in European Union and other countries where strict legislations on GMOs were set up. Performance of the methods used in laboratories around the world should be uniform, in order to obtain reliable and comparable results. Accreditation is a suitable system for harmonising procedures in each testing laboratory. In this paper, key elements for the accreditation of molecular biology methods for GMO detection according to ISO/IEC 17025 are described. The procedures described are also valuable for the accreditation of molecular methods for all laboratory diagnostics where qualitative and quantitative characterisation of nucleic acids is needed.
Keywords: Accreditation; Genetically modified organisms; Molecular methods; Quantitative PCR; Quality assurance
Corrosion and Quality by Alec Groysman; Naphtali Brodsky (pp. 537-542).
Corrosion is an interaction between a material and its environment that results in deterioration of both. Quality has a wider meaning and designates the suitability of products, management quality and work. Corrosion is a phenomenon, and quality is a
Keywords: philosophical category. The aim of this work is to find common ground between corrosion and quality. We encounter degradation of materials and the environment in everyday life. Corrosion influences the quality of work, products, management, environment and life. The aspects of corrosion correspond to the various meanings of quality. Corrosion costs may be considered as part of the total costs of quality. Corrosion costs are estimated to be as high as 5% of the GNP in various countries.Most corrosion costs can be saved and quality improved by means of control measures, analysis of failures, dissemination of knowledge, and use of monitoring techniques. Anti-corrosion management quality includes design, manufacture, improvement, and control at all stages.
Corrosion and Quality by Alec Groysman; Naphtali Brodsky (pp. 537-542).
Corrosion is an interaction between a material and its environment that results in deterioration of both. Quality has a wider meaning and designates the suitability of products, management quality and work. Corrosion is a phenomenon, and quality is a
Keywords: philosophical category. The aim of this work is to find common ground between corrosion and quality. We encounter degradation of materials and the environment in everyday life. Corrosion influences the quality of work, products, management, environment and life. The aspects of corrosion correspond to the various meanings of quality. Corrosion costs may be considered as part of the total costs of quality. Corrosion costs are estimated to be as high as 5% of the GNP in various countries.Most corrosion costs can be saved and quality improved by means of control measures, analysis of failures, dissemination of knowledge, and use of monitoring techniques. Anti-corrosion management quality includes design, manufacture, improvement, and control at all stages.
Assessment and assurance of quality in water measurement by coulometric Karl Fischer titration of petroleum products by Pavlina G. Ivanova; Zara V. Aneva (pp. 543-549).
The precise and accurate determination of water in petroleum products—gasoline, diesel oil and aromatic hydrocarbons—is of significant importance for their normal functional and operational characteristics for economics as well as in meeting international requirements. The standard method ISO 12937 for the measurement of water by the coulometric Karl Fischer titration method was subject to within-laboratory assessment. Thereby it was established that the analytical procedure could not always be relied upon, especially when low levels of water were determined. The aim of this work is to assess each stage of the test procedure depending on the particular problems defined by the samples, using high-reactive Karl Fischer reagents and coulometric cells with and without a diaphragm, and to indicate the major factors causing the uncertainty. A reduced combined uncertainty was achieved by modifying the sample preparation step, the administration of the moisture in the coulometric cell, and sample injection manipulation. Experiments showed that the cell without the diaphragm ensures lower and uniform uncertainty of the measurements in the range of 0.01 to 10 mg H2O in comparison to the cell with a diaphragm and therefore is more appropriate for the determination of low water levels in the petroleum products. A procedure that utilized a mixture of the reagent and toluene (10:6) was able to resolve the problem of two phases of formation and reduced conductivity of the reagent in direct titration of diesel oils. The results suggest that the modified procedure ensures relative expanded uncertainty equal to or less than 2.0% (n=5, confidence interval close to 95%) and 99.4% recovery for petroleum products investigated in repeatability conditions.
Keywords: Water determination; Coulometric Karl Fischer titration; Petroleum products
Assessment and assurance of quality in water measurement by coulometric Karl Fischer titration of petroleum products by Pavlina G. Ivanova; Zara V. Aneva (pp. 543-549).
The precise and accurate determination of water in petroleum products—gasoline, diesel oil and aromatic hydrocarbons—is of significant importance for their normal functional and operational characteristics for economics as well as in meeting international requirements. The standard method ISO 12937 for the measurement of water by the coulometric Karl Fischer titration method was subject to within-laboratory assessment. Thereby it was established that the analytical procedure could not always be relied upon, especially when low levels of water were determined. The aim of this work is to assess each stage of the test procedure depending on the particular problems defined by the samples, using high-reactive Karl Fischer reagents and coulometric cells with and without a diaphragm, and to indicate the major factors causing the uncertainty. A reduced combined uncertainty was achieved by modifying the sample preparation step, the administration of the moisture in the coulometric cell, and sample injection manipulation. Experiments showed that the cell without the diaphragm ensures lower and uniform uncertainty of the measurements in the range of 0.01 to 10 mg H2O in comparison to the cell with a diaphragm and therefore is more appropriate for the determination of low water levels in the petroleum products. A procedure that utilized a mixture of the reagent and toluene (10:6) was able to resolve the problem of two phases of formation and reduced conductivity of the reagent in direct titration of diesel oils. The results suggest that the modified procedure ensures relative expanded uncertainty equal to or less than 2.0% (n=5, confidence interval close to 95%) and 99.4% recovery for petroleum products investigated in repeatability conditions.
Keywords: Water determination; Coulometric Karl Fischer titration; Petroleum products
Estimation of sample processing uncertainty for chlorpyrifos residue in cucumber by Osman Tiryaki; Dilan Baysoyu (pp. 550-553).
Sample processing is a very important component of uncertainty in analytical results. In order to have reliable results, the laboratory sample should be properly processed to obtain statistically homogenous matrix—before the representative test portions are withdrawn for analysis. The use of 14C-labeled compound is preferable because the analyte can be quantified without cleanup. The method is based on surface treatment of cucumber with 14C-chlorpyrifos, determination of 14C-chlorpyrifos activity in the replicate test portions of different size, and determination of the uncertainty of sample processing.
Keywords: Sample processing; Uncertainty; Sampling constant
Estimation of sample processing uncertainty for chlorpyrifos residue in cucumber by Osman Tiryaki; Dilan Baysoyu (pp. 550-553).
Sample processing is a very important component of uncertainty in analytical results. In order to have reliable results, the laboratory sample should be properly processed to obtain statistically homogenous matrix—before the representative test portions are withdrawn for analysis. The use of 14C-labeled compound is preferable because the analyte can be quantified without cleanup. The method is based on surface treatment of cucumber with 14C-chlorpyrifos, determination of 14C-chlorpyrifos activity in the replicate test portions of different size, and determination of the uncertainty of sample processing.
Keywords: Sample processing; Uncertainty; Sampling constant
IMEP in support of the comparability of measurement results across the Romanian chemical metrology infrastructure by S. Duta; Y. Aregbe; L. Van Nevel; P. Taylor; F. Iacobescu (pp. 554-561).
On the basis of quantitative chemical measurements many important decisions are made in support of legislation or in industrial processes or social aspects. For this reason it is important to improve the quality of chemical measurement results and thus make them comparable and acceptable everywhere. The measurement quality is important to enable an equivalent implementation of the European Union regulations and directives across an enlarged EU. In this context, the European Commission–Joint Research Centre–Institute for Reference Materials and Measurement (EC-JRC-IRMM) set up a programme to improve the scientific basis for metrology in chemistry (MiC) in EU candidate countries in the framework of EU enlargement. Several activities were initiated, such as training, fellowships, sponsoring of seminars, conferences and participation in interlaboratory comparisons. To disseminate measurement traceability, IRMM provides through its International Measurement Evaluation Programme (IMEP) an interlaboratory tool to enable the benchmarking of laboratory performance. IMEP emphasizes the metrological aspects of measurement results, such as traceability and measurement uncertainty. In this way it has become a publicly available European tool for MiC. The Romanian Bureau of Legal Metrology – National Institute of Metrology (BRML-INM) actively supports the participation of Romanian authorized and field laboratories in IMEP interlaboratory comparisons. This paper describes the interest of Romanian laboratories participating in this programme, the analytical and metrological problems that became relevant during these exercises and some actions for improvement. The results from Romanian laboratories participating in IMEP-12 (water), IMEP-16 (wine), IMEP-17 (human serum) and IMEP-20 (tuna fish) are presented. To conclude, the educational and training activities at national level organized jointly by the Romanian National Institute of Metrology (INM) and IRMM are also mentioned.
Keywords: IMEP; Comparability of results; Metrology in chemistry
IMEP in support of the comparability of measurement results across the Romanian chemical metrology infrastructure by S. Duta; Y. Aregbe; L. Van Nevel; P. Taylor; F. Iacobescu (pp. 554-561).
On the basis of quantitative chemical measurements many important decisions are made in support of legislation or in industrial processes or social aspects. For this reason it is important to improve the quality of chemical measurement results and thus make them comparable and acceptable everywhere. The measurement quality is important to enable an equivalent implementation of the European Union regulations and directives across an enlarged EU. In this context, the European Commission–Joint Research Centre–Institute for Reference Materials and Measurement (EC-JRC-IRMM) set up a programme to improve the scientific basis for metrology in chemistry (MiC) in EU candidate countries in the framework of EU enlargement. Several activities were initiated, such as training, fellowships, sponsoring of seminars, conferences and participation in interlaboratory comparisons. To disseminate measurement traceability, IRMM provides through its International Measurement Evaluation Programme (IMEP) an interlaboratory tool to enable the benchmarking of laboratory performance. IMEP emphasizes the metrological aspects of measurement results, such as traceability and measurement uncertainty. In this way it has become a publicly available European tool for MiC. The Romanian Bureau of Legal Metrology – National Institute of Metrology (BRML-INM) actively supports the participation of Romanian authorized and field laboratories in IMEP interlaboratory comparisons. This paper describes the interest of Romanian laboratories participating in this programme, the analytical and metrological problems that became relevant during these exercises and some actions for improvement. The results from Romanian laboratories participating in IMEP-12 (water), IMEP-16 (wine), IMEP-17 (human serum) and IMEP-20 (tuna fish) are presented. To conclude, the educational and training activities at national level organized jointly by the Romanian National Institute of Metrology (INM) and IRMM are also mentioned.
Keywords: IMEP; Comparability of results; Metrology in chemistry
in situ interlaboratory comparisons for dissolved oxygen concentration and pH by Lauri Jalukse; Viktor Vabson; Ivo Leito (pp. 562-564).
Organization, benefits, and possible drawbacks of in situ interlaboratory comparison are discussed using the example of dissolved oxygen concentration and pH measurements organized at the University of Tartu. In situ interlaboratory comparisons are intercomparison measurements, where all the participants (with their technical equipment and using their own competence) are measuring the same sample continuously at the same time, at the same site. In the field of proficiency testing–especially in chemical measurements–the in situ schemes are not yet widespread. Their main advantage emerges in the fields where, due to non-stability of samples, traditional comparison schemes can fail. Direct exchange of experience between the participants and presentations during measurements may add the value to in situ interlaboratory comparison.Dissolved oxygen concentration and pH measurements are among the most widespread chemical measurements. Both measurements are complex and less robust than often considered. In this paper, we describe in situ interlaboratory comparisons of dissolved oxygen concentration and pH organized at University of Tartu Testing Centre.
Keywords: In situ interlaboratory comparison; Proficiency testing; Dissolved oxygen; pH
in situ interlaboratory comparisons for dissolved oxygen concentration and pH by Lauri Jalukse; Viktor Vabson; Ivo Leito (pp. 562-564).
Organization, benefits, and possible drawbacks of in situ interlaboratory comparison are discussed using the example of dissolved oxygen concentration and pH measurements organized at the University of Tartu. In situ interlaboratory comparisons are intercomparison measurements, where all the participants (with their technical equipment and using their own competence) are measuring the same sample continuously at the same time, at the same site. In the field of proficiency testing–especially in chemical measurements–the in situ schemes are not yet widespread. Their main advantage emerges in the fields where, due to non-stability of samples, traditional comparison schemes can fail. Direct exchange of experience between the participants and presentations during measurements may add the value to in situ interlaboratory comparison.Dissolved oxygen concentration and pH measurements are among the most widespread chemical measurements. Both measurements are complex and less robust than often considered. In this paper, we describe in situ interlaboratory comparisons of dissolved oxygen concentration and pH organized at University of Tartu Testing Centre.
Keywords: In situ interlaboratory comparison; Proficiency testing; Dissolved oxygen; pH
Determination of the method detection limits for acid extractable metals in environmental solids: a comparative approach by X. J. Yang; G. K.-C. Low (pp. 565-573).
The accurate determination of method detection limits (MDLs) for acid extractable metals in environmental solid samples (soils, sediments and solid wastes) has been shown to be difficult because not only is it difficult to obtain a representative reference soil sample but also sample spiking is difficult. The use of reagent water as the reference matrix for the determination of MDL in soils does not reflect the matrix effect of real world samples. This paper proposes a comparative approach for determining MDLs for acid extractable metals in soils by first comparing the MDL derived from environmental surface waters with the MDL estimated from the replicate analyses of real soil samples, before assigning a rational MDL values for use in soils. This comparative approach does not require spiking soil and provides more realistic MDL values than the reagent water-based MDLs because they reflect the matrix effect of soils. This paper also provides a method for quantitative description of the matrix effect, which has been a qualitative description in the literature to date. The assigned MDL is verified using the relative standard deviation (RSD) obtained from the analysis of soils of different textures.
Keywords: Method detection limit; Acid extractable metals; Environmental solids; ICP-AES
Determination of the method detection limits for acid extractable metals in environmental solids: a comparative approach by X. J. Yang; G. K.-C. Low (pp. 565-573).
The accurate determination of method detection limits (MDLs) for acid extractable metals in environmental solid samples (soils, sediments and solid wastes) has been shown to be difficult because not only is it difficult to obtain a representative reference soil sample but also sample spiking is difficult. The use of reagent water as the reference matrix for the determination of MDL in soils does not reflect the matrix effect of real world samples. This paper proposes a comparative approach for determining MDLs for acid extractable metals in soils by first comparing the MDL derived from environmental surface waters with the MDL estimated from the replicate analyses of real soil samples, before assigning a rational MDL values for use in soils. This comparative approach does not require spiking soil and provides more realistic MDL values than the reagent water-based MDLs because they reflect the matrix effect of soils. This paper also provides a method for quantitative description of the matrix effect, which has been a qualitative description in the literature to date. The assigned MDL is verified using the relative standard deviation (RSD) obtained from the analysis of soils of different textures.
Keywords: Method detection limit; Acid extractable metals; Environmental solids; ICP-AES
The variance of a consensus by Michael Thompson (pp. 574-575).
In proficiency tests the consensus of the participants' results is often used as the assigned value to calculate z-scores. Where the consensus is quantified as the robust mean $$hatmu_{{
m rob}}$$ of n results, the standard error of the assigned value is often taken to be $${{hatsigma_{{
m rob}}}mathord{left/{vphantom{{hatsigma_{{
m rob}}}{sqrt n}}}
ight. kern-
ulldelimiterspace}{sqrt n}}$$ , where $$hatsigma_{{
m rob}}$$ is the robust standard deviation estimated from the same data 1 . As some of the results are downweighted in robust estimation, $$sqrt n$$ is too large a denominator, so that $${{hatsigma_{{
m rob}}}mathord{left/{vphantom{{hatsigma_{{
m rob}}}{sqrt n}}}
ight. kern-
ulldelimiterspace}{sqrt n}}$$ tends to have a somewhat low bias. This bias is shown to be inconsequential for proficiency testing purposes. However, an unbiased estimate can be obtained by using the bootstrap.
The variance of a consensus by Michael Thompson (pp. 574-575).
In proficiency tests the consensus of the participants' results is often used as the assigned value to calculate z-scores. Where the consensus is quantified as the robust mean $$hatmu_{{
m rob}}$$ of n results, the standard error of the assigned value is often taken to be $${{hatsigma_{{
m rob}}}mathord{left/{vphantom{{hatsigma_{{
m rob}}}{sqrt n}}}
ight. kern-
ulldelimiterspace}{sqrt n}}$$ , where $$hatsigma_{{
m rob}}$$ is the robust standard deviation estimated from the same data 1 . As some of the results are downweighted in robust estimation, $$sqrt n$$ is too large a denominator, so that $${{hatsigma_{{
m rob}}}mathord{left/{vphantom{{hatsigma_{{
m rob}}}{sqrt n}}}
ight. kern-
ulldelimiterspace}{sqrt n}}$$ tends to have a somewhat low bias. This bias is shown to be inconsequential for proficiency testing purposes. However, an unbiased estimate can be obtained by using the bootstrap.
New definitions on reference materials by Hendrik Emons; Ales Fajgelj; Adriaan M. H. van der Veen; Robert Watters (pp. 576-578).
The new definitions for reference material and certified reference material as approved by ISO REMCO are provided and further explained.
Keywords: Reference material; Certified reference material; Terminology; Harmonization
New definitions on reference materials by Hendrik Emons; Ales Fajgelj; Adriaan M. H. van der Veen; Robert Watters (pp. 576-578).
The new definitions for reference material and certified reference material as approved by ISO REMCO are provided and further explained.
Keywords: Reference material; Certified reference material; Terminology; Harmonization