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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #8)


International Atomic Energy Agency's contributions to advances in nutritional and environmental metrology by G. V. Iyengar; R. M. Parr (pp. 393-402).
For more than three decades the International Atomic Energy Agency (IAEA) has supported projects on food, nutrition and environment for strengthening the analytical capabilities in developing countries (DCs). Over time, such efforts have led to the development of proper study designs, harmonization of sampling protocols, adequate contamination control and evaluation of the suitability of competing analytical techniques for the determination of specific analytes. Collectively, these consistent IAEA initiatives have promoted harmonization of chemical measurements thus facilitating comparability of results of filed investigations. Importantly, the Agency's efforts have infused a measure of metrological awareness in measurements carried out in field studies, including physiological measurements. Nuclear and isotopic techniques have played an important role in reaching these goals by establishing reliable measurement processes for application in health care studies.

Keywords: Metrology; Nutrition and environmental metrology; Harmonization of chemical measurements; Nuclear and isotopic techniques; Analytical quality assurance; Physiological measurements


International Atomic Energy Agency's contributions to advances in nutritional and environmental metrology by G. V. Iyengar; R. M. Parr (pp. 393-402).
For more than three decades the International Atomic Energy Agency (IAEA) has supported projects on food, nutrition and environment for strengthening the analytical capabilities in developing countries (DCs). Over time, such efforts have led to the development of proper study designs, harmonization of sampling protocols, adequate contamination control and evaluation of the suitability of competing analytical techniques for the determination of specific analytes. Collectively, these consistent IAEA initiatives have promoted harmonization of chemical measurements thus facilitating comparability of results of filed investigations. Importantly, the Agency's efforts have infused a measure of metrological awareness in measurements carried out in field studies, including physiological measurements. Nuclear and isotopic techniques have played an important role in reaching these goals by establishing reliable measurement processes for application in health care studies.

Keywords: Metrology; Nutrition and environmental metrology; Harmonization of chemical measurements; Nuclear and isotopic techniques; Analytical quality assurance; Physiological measurements


Verification of uncertainty budgets by Kaj Heydorn; Birger Stjernholm Madsen (pp. 403-408).
The quality of analytical results is expressed by their uncertainty, as it is estimated on the basis of an uncertainty budget; little effort is, however, often spent on ascertaining the quality of the uncertainty budget. The uncertainty budget is based on circumstantial or historical data, and therefore it is essential that the applicability of the overall uncertainty budget to actual measurement results be verified on the basis of current experimental data. This should be carried out by replicate analysis of samples taken in accordance with the definition of the measurand, but representing the full range of matrices and concentrations for which the budget is assumed to be valid. In this way the assumptions made in the uncertainty budget can be experimentally verified, both as regards sources of variability that are assumed negligible, and dominant uncertainty components. Agreement between observed and expected variability is tested by means of the T-test, which follows a chi-square distribution with a number of degrees of freedom determined by the number of replicates. Significant deviations between predicted and observed variability may be caused by a variety of effects, and examples will be presented; both underestimation and overestimation may occur, each leading to correcting the influence of uncertainty components according to their influence on the variability of experimental results. Some uncertainty components can be verified only with a very small number of degrees of freedom, because their influence requires samples taken at long intervals, e.g., the acquisition of a new calibrant. It is therefore recommended to include verification of the uncertainty budget in the continuous QA/QC monitoring; this will eventually lead to a test also for such rarely occurring effects.

Keywords: Uncertainty budget; Verification; Process control; T-statistic


Verification of uncertainty budgets by Kaj Heydorn; Birger Stjernholm Madsen (pp. 403-408).
The quality of analytical results is expressed by their uncertainty, as it is estimated on the basis of an uncertainty budget; little effort is, however, often spent on ascertaining the quality of the uncertainty budget. The uncertainty budget is based on circumstantial or historical data, and therefore it is essential that the applicability of the overall uncertainty budget to actual measurement results be verified on the basis of current experimental data. This should be carried out by replicate analysis of samples taken in accordance with the definition of the measurand, but representing the full range of matrices and concentrations for which the budget is assumed to be valid. In this way the assumptions made in the uncertainty budget can be experimentally verified, both as regards sources of variability that are assumed negligible, and dominant uncertainty components. Agreement between observed and expected variability is tested by means of the T-test, which follows a chi-square distribution with a number of degrees of freedom determined by the number of replicates. Significant deviations between predicted and observed variability may be caused by a variety of effects, and examples will be presented; both underestimation and overestimation may occur, each leading to correcting the influence of uncertainty components according to their influence on the variability of experimental results. Some uncertainty components can be verified only with a very small number of degrees of freedom, because their influence requires samples taken at long intervals, e.g., the acquisition of a new calibrant. It is therefore recommended to include verification of the uncertainty budget in the continuous QA/QC monitoring; this will eventually lead to a test also for such rarely occurring effects.

Keywords: Uncertainty budget; Verification; Process control; T-statistic


Evaluation of the use of consensus values in proficiency testing programmes by Siu Kay Wong (pp. 409-414).
Proficiency testing (PT) is an essential tool used by laboratory accreditation bodies to assess the competency of laboratories. Because of limited resources of PT providers or for other reasons, the assigned reference value used in the calculation of z-score values has usually been derived from some sort of consensus value obtained by central tendency estimators such as the arithmetic mean or robust mean. However, if the assigned reference value deviates significantly from the ‘true value’ of the analyte in the test material, laboratories’ performance will be evaluated incorrectly. This paper evaluates the use of consensus values in proficiency testing programmes using the Monte Carlo simulation technique. The results indicated that the deviation of the assigned value from the true value could be as large as 40%, depending on the parameters of the proficiency testing programmes under investigation such as sample homogeneity, number of participant laboratories, concentration level, method precision and laboratory bias. To study how these parameters affect the degree of discrepancy between the consensus value and the true value, a fractional factorial design was also applied. The findings indicate that the number of participating laboratories and the distribution of laboratory bias were the prime two factors affecting the deviation of the consensus value from the true value.

Keywords: Proficiency testing; Monte Carlo simulation; Central tendency estimator; Consensus value; Experiment design


Evaluation of the use of consensus values in proficiency testing programmes by Siu Kay Wong (pp. 409-414).
Proficiency testing (PT) is an essential tool used by laboratory accreditation bodies to assess the competency of laboratories. Because of limited resources of PT providers or for other reasons, the assigned reference value used in the calculation of z-score values has usually been derived from some sort of consensus value obtained by central tendency estimators such as the arithmetic mean or robust mean. However, if the assigned reference value deviates significantly from the ‘true value’ of the analyte in the test material, laboratories’ performance will be evaluated incorrectly. This paper evaluates the use of consensus values in proficiency testing programmes using the Monte Carlo simulation technique. The results indicated that the deviation of the assigned value from the true value could be as large as 40%, depending on the parameters of the proficiency testing programmes under investigation such as sample homogeneity, number of participant laboratories, concentration level, method precision and laboratory bias. To study how these parameters affect the degree of discrepancy between the consensus value and the true value, a fractional factorial design was also applied. The findings indicate that the number of participating laboratories and the distribution of laboratory bias were the prime two factors affecting the deviation of the consensus value from the true value.

Keywords: Proficiency testing; Monte Carlo simulation; Central tendency estimator; Consensus value; Experiment design


Traceability in quantitative NMR using an electronic signal as working standard by Gérald S. Remaud; Virginie Silvestre; Serge Akoka (pp. 415-420).
The choice of the reference, either as internal or external is not straightforward in quantitative NMR. In this context ERETIC™ methodology appears as an universal referencing technique. An electronic signal, generated by the NMR spectrometer during the acquisition time, operates as a virtual working standard. The processes for ensuring a traceability to primary standards is illustrated on the official method devoted to (D/H)i ratios measurement on ethanol, using quantitative 2H-NMR. The ERETIC approach is shown to be equivalent to its official homologue, in terms of accuracy and precision. Finally, its performance could be beneficial to other analytes, matrices and nuclei.

Keywords: Quantitative NMR; ERETIC; SNIF-NMR; Traceability; Reference materials


Traceability in quantitative NMR using an electronic signal as working standard by Gérald S. Remaud; Virginie Silvestre; Serge Akoka (pp. 415-420).
The choice of the reference, either as internal or external is not straightforward in quantitative NMR. In this context ERETIC™ methodology appears as an universal referencing technique. An electronic signal, generated by the NMR spectrometer during the acquisition time, operates as a virtual working standard. The processes for ensuring a traceability to primary standards is illustrated on the official method devoted to (D/H)i ratios measurement on ethanol, using quantitative 2H-NMR. The ERETIC approach is shown to be equivalent to its official homologue, in terms of accuracy and precision. Finally, its performance could be beneficial to other analytes, matrices and nuclei.

Keywords: Quantitative NMR; ERETIC; SNIF-NMR; Traceability; Reference materials


Structure analytical methods for quantitative reference applications by H. Jancke; F. Malz; W. Haesselbarth (pp. 421-429).
The analytical methods mass spectrometry, UV/Vis, IR, Raman, Fluorometry, XRD, Mössbauer, and NMR used to elucidate chemical structure are evaluated regarding their capabilities to be used as primary analytical techniques in quantitative measurements, considering the criteria in the CCQM definition of primary methods. This includes a review of the respective measurement equations, the evaluation of the measurement uncertainty, and a discussion of evidence for the “highest metrological level”, as obtained from intercomparisons in contest with other methods. It is shown that only few methods fulfill the CCQM criteria. Quantitative NMR spectroscopy is one of them and may be considered as a potential primary method as recommended by CCQM because of being free of empirical factors in the uncertainty budget.

Keywords: Metrology; Structure analysis; Quantitative analysis; Primary methods; Reference methods


Structure analytical methods for quantitative reference applications by H. Jancke; F. Malz; W. Haesselbarth (pp. 421-429).
The analytical methods mass spectrometry, UV/Vis, IR, Raman, Fluorometry, XRD, Mössbauer, and NMR used to elucidate chemical structure are evaluated regarding their capabilities to be used as primary analytical techniques in quantitative measurements, considering the criteria in the CCQM definition of primary methods. This includes a review of the respective measurement equations, the evaluation of the measurement uncertainty, and a discussion of evidence for the “highest metrological level”, as obtained from intercomparisons in contest with other methods. It is shown that only few methods fulfill the CCQM criteria. Quantitative NMR spectroscopy is one of them and may be considered as a potential primary method as recommended by CCQM because of being free of empirical factors in the uncertainty budget.

Keywords: Metrology; Structure analysis; Quantitative analysis; Primary methods; Reference methods


Uncertainty of measurement for the determination of fluoride in water and wastewater by direct selective electrode potentiometry by Ana R. Sousa; Maria A. Trancoso (pp. 430-438).
A procedure to estimate the uncertainty of measurement applied to the fluoride determination of waters and wastewaters matrices by selective electrode potentiometry was implemented based on Eurachem Guide. The major sources of uncertainty were identified as the calibration standard solutions, fluoride concentration obtained by potential interpolation of the regression line and the precision. However the relative uncertainties depend on the anion concentration levels. The methodology proposed was presented to two fluoride concentration levels that are in the range of surface water samples (C sample=1.12 mgF l−1) and of wastewater matrices (C sample=101.4 mgF l−1). The expanded uncertainties calculated were 0.40 and 9.1 mg l−1 for low and high concentration levels, respectively, using the reproducibility uncertainty as precision evaluation. The relative expanded uncertainty was around ±10% for the highest concentration, which can be considered acceptable for the ion selective electrode potenciometric methods and ±36% for the lowest concentrations. In this case the sample fluoride content is very close to the limit of quantification which has a relative uncertainty of about ±30%. If the repeatability was used in spite of duplicate analysis the same conclusions were obtained (C sample=1.12 ± 0.39 mgF l−1 and C sample=101.4 ± 7.0 mgF l−1).Although the calculated expanded uncertainties and consequently the combined uncertainty, do not vary significantly in the cases where it was used the repeatability or reproducibility for evaluating the precision, each relative variances uncertainty contributions do. When the repeatability is used to determine the combined uncertainty, the CSS and $$ C_{{ m F}^ - }$$ uncertainties contributions are the most dominant ones. However, if reproducibility is used, relative uncertainty variance contributions are distributed among CSS, C F, and precision. In both cases, the $$ r_{c_{ m F} }$$ contribution increases and r CSS contribution decreases with the increasing of the concentration level. The precision variance contribution is only significant in the case where the reproducibility is used, and increases with the increasing of the concentration level. The uncertainty in the result calculated using the proposed methodology (C sample ± U sample = 2.17 ± 0.42 mgF l−1) is in satisfactory agreement with the estimated expanded uncertainty obtained using the relative reproducibility standard deviation obtained in interlaboratory studies ( $$ C_{{ m sample}} pm U_{C_{{ m sample}} } = 2.17 pm 0.44,{ m mg},{ m F},,{ m l}^{{ m - 1}}$$ ).

Keywords: Measurement uncertainty; Uncertainty component; Water and wastewater analysis; Ion selective electrodes; Fluoride


Uncertainty of measurement for the determination of fluoride in water and wastewater by direct selective electrode potentiometry by Ana R. Sousa; Maria A. Trancoso (pp. 430-438).
A procedure to estimate the uncertainty of measurement applied to the fluoride determination of waters and wastewaters matrices by selective electrode potentiometry was implemented based on Eurachem Guide. The major sources of uncertainty were identified as the calibration standard solutions, fluoride concentration obtained by potential interpolation of the regression line and the precision. However the relative uncertainties depend on the anion concentration levels. The methodology proposed was presented to two fluoride concentration levels that are in the range of surface water samples (C sample=1.12 mgF l−1) and of wastewater matrices (C sample=101.4 mgF l−1). The expanded uncertainties calculated were 0.40 and 9.1 mg l−1 for low and high concentration levels, respectively, using the reproducibility uncertainty as precision evaluation. The relative expanded uncertainty was around ±10% for the highest concentration, which can be considered acceptable for the ion selective electrode potenciometric methods and ±36% for the lowest concentrations. In this case the sample fluoride content is very close to the limit of quantification which has a relative uncertainty of about ±30%. If the repeatability was used in spite of duplicate analysis the same conclusions were obtained (C sample=1.12 ± 0.39 mgF l−1 and C sample=101.4 ± 7.0 mgF l−1).Although the calculated expanded uncertainties and consequently the combined uncertainty, do not vary significantly in the cases where it was used the repeatability or reproducibility for evaluating the precision, each relative variances uncertainty contributions do. When the repeatability is used to determine the combined uncertainty, the CSS and $$ C_{{ m F}^ - }$$ uncertainties contributions are the most dominant ones. However, if reproducibility is used, relative uncertainty variance contributions are distributed among CSS, C F, and precision. In both cases, the $$ r_{c_{ m F} }$$ contribution increases and r CSS contribution decreases with the increasing of the concentration level. The precision variance contribution is only significant in the case where the reproducibility is used, and increases with the increasing of the concentration level. The uncertainty in the result calculated using the proposed methodology (C sample ± U sample = 2.17 ± 0.42 mgF l−1) is in satisfactory agreement with the estimated expanded uncertainty obtained using the relative reproducibility standard deviation obtained in interlaboratory studies ( $$ C_{{ m sample}} pm U_{C_{{ m sample}} } = 2.17 pm 0.44,{ m mg},{ m F},,{ m l}^{{ m - 1}}$$ ).

Keywords: Measurement uncertainty; Uncertainty component; Water and wastewater analysis; Ion selective electrodes; Fluoride


Quality control procedures for chloride and nitrate ions analysis in plant samples by ion chromatography by Pierre Masson; Fabrice de Raemaeker; Fatima Bon (pp. 439-443).
This paper describes useful procedures to monitor quality of chloride and nitrate ions analysis in plant samples by ion chromatography. The use of certified reference materials (CRMs) provided an efficient way to verify the accuracy of the method. Data generated by the method of analysis for chloride compared favourably with certified values. The quality system included also the systematic analysis of an internal reference sample in each batch of samples routinely analysed. The performance of the method, including extraction and measurement, over a period of 3 years was reported with control charts. The yearly variation coefficients were less than 6.5% for chloride and nitrate ions. Finally, the analytical method was evaluated through the participation of laboratory to an international proficiency testing scheme. Found results were not significantly different from published medians.

Keywords: Plant samples; Inorganic anions; Ion chromatography; Quality control


Quality control procedures for chloride and nitrate ions analysis in plant samples by ion chromatography by Pierre Masson; Fabrice de Raemaeker; Fatima Bon (pp. 439-443).
This paper describes useful procedures to monitor quality of chloride and nitrate ions analysis in plant samples by ion chromatography. The use of certified reference materials (CRMs) provided an efficient way to verify the accuracy of the method. Data generated by the method of analysis for chloride compared favourably with certified values. The quality system included also the systematic analysis of an internal reference sample in each batch of samples routinely analysed. The performance of the method, including extraction and measurement, over a period of 3 years was reported with control charts. The yearly variation coefficients were less than 6.5% for chloride and nitrate ions. Finally, the analytical method was evaluated through the participation of laboratory to an international proficiency testing scheme. Found results were not significantly different from published medians.

Keywords: Plant samples; Inorganic anions; Ion chromatography; Quality control


Estimation scheme for level-dependent uncertainty of analytical result: application for determination of 1-hydroxypyrene in urine by Žydrė Šaltienė; Natalija Jatulienė; Mudis Šalkauskas; Daiva Brukštienė; Asta Ruzgytė; Aušra Tarasevičiūtė; Julius Kalibatas (pp. 444-451).
The estimation scheme of uncertainty of determination of 1-hydroxypyrene (1-OHP) in urine was developed analysing the main stages of the analytical procedure: (1) preparation of 1-OHP standards, (2) creation of the calibration curve for the high performance liquid chromatography (HPLC) analysis method with the evaluation of recovery, (3) measuring procedure of aliquot of urine, (4) adjusting the pH of aliquot and hydrolysis with enzyme, (5) solid phase extraction, (6) concentration of the extract, (7) injection of the extract to chromatograph and analysing by the HPLC method, (8) calculation of 1-OHP mass from the calibration curve, (9) calculation of 1-OHP concentration in urine. The evaluation of the uncertainty is based on quantification of individual components. Combined uncertainty was calculated using the law of propagation of uncertainties according to the EURACHEM/CITAC guidelines. Level dependence of the uncertainty arises from the calibration curve.The limits of detection and quantification were found to be equal to 0.03 and 0.1 ng/mL, respectively. The calculated expanded level-dependent uncertainty covers 47–27–25% within the concentration range 0.03–0.1–0.4 ng/mL with the materials and equipment used. These parameters could easily be recalculated according to the proposed scheme if there are some changes in the analysis procedure.

Keywords: Uncertainty; Level-dependent uncertainty; 1-Hydroxypyrene; Biomarker; PAHs


Estimation scheme for level-dependent uncertainty of analytical result: application for determination of 1-hydroxypyrene in urine by Žydrė Šaltienė; Natalija Jatulienė; Mudis Šalkauskas; Daiva Brukštienė; Asta Ruzgytė; Aušra Tarasevičiūtė; Julius Kalibatas (pp. 444-451).
The estimation scheme of uncertainty of determination of 1-hydroxypyrene (1-OHP) in urine was developed analysing the main stages of the analytical procedure: (1) preparation of 1-OHP standards, (2) creation of the calibration curve for the high performance liquid chromatography (HPLC) analysis method with the evaluation of recovery, (3) measuring procedure of aliquot of urine, (4) adjusting the pH of aliquot and hydrolysis with enzyme, (5) solid phase extraction, (6) concentration of the extract, (7) injection of the extract to chromatograph and analysing by the HPLC method, (8) calculation of 1-OHP mass from the calibration curve, (9) calculation of 1-OHP concentration in urine. The evaluation of the uncertainty is based on quantification of individual components. Combined uncertainty was calculated using the law of propagation of uncertainties according to the EURACHEM/CITAC guidelines. Level dependence of the uncertainty arises from the calibration curve.The limits of detection and quantification were found to be equal to 0.03 and 0.1 ng/mL, respectively. The calculated expanded level-dependent uncertainty covers 47–27–25% within the concentration range 0.03–0.1–0.4 ng/mL with the materials and equipment used. These parameters could easily be recalculated according to the proposed scheme if there are some changes in the analysis procedure.

Keywords: Uncertainty; Level-dependent uncertainty; 1-Hydroxypyrene; Biomarker; PAHs
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