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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.17, #3)
Interlaboratory comparison of test results of an ordinal or nominal binary property: analysis of variation by Emil Bashkansky; Tamar Gadrich; Ilya Kuselman (pp. 239-243).
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.
Keywords: Analysis of variance; Ordinal property; Nominal property; Interlaboratory comparison; Proficiency testing; Reference materials; Method validation
A pilot study (APMP.QM-P19) for the measurement of melamine in milk powder by Della W. M. Sin; Pui-kwan Chan; Yiu-chung Wong; Xiu-qing Li; Qinhe Zhang (pp. 245-251).
A pilot study (APMP.QM-P19) of the Asia Pacific Metrology Program for the determination of melamine at two different levels in milk powder was organized in 2010. It was the first interlaboratory comparison programme in measuring melamine in food matrices for metrology institutes in the region. Melamine was chosen as the target analyte because of the recent crises that happened in 2007 and 2008 had caused substantial concern from consumers, food manufacturers, policy makers on food safety and the food testing communities. The objectives of APMP.QM-P19 were to evaluate the testing capability of participants on the quantification of trace level melamine in milk and milk products and to investigate the degree of equivalence with respect to the assigned values. In total, 19 laboratories (11 metrology institutes and eight food testing institutes) enrolled in the study. Analytical techniques reported by participants included liquid chromatography with ultra-violet and tandem mass spectrometry, gas chromatography with high-resolution mass spectrometry and enzyme-linked immunosorbent assay. Dispersion of analytical data in the two test materials was significant, and normal Gaussian distribution of data was not observed. The median was agreed to be used as the assigned values in the programme. Metrology institutes who employed isotope dilution mass spectrometry technique were found to give more consistent results and higher degree of equivalence than others. The performance of most of the food testing institutes was not satisfactory, and they were encouraged to have a thorough review of their validation procedure and estimation of uncertainty.
Keywords: Melamine; Milk powder; APMP; Pilot study; Interlaboratory comparison
Trace analysis of small gas samples in sealed containers with mass spectrometry using static dilution by Hans-Peter Haerri; Timothée Deblock; Pierre Pringalle; José Garcia; Andreas Ackermann; Cédric Couret (pp. 253-264).
A sampling method for the analysis of small amounts of gases from sealed containers is described. Liquefied pressurised gas samples were expanded into a vacuum box and statically diluted with ultrapure nitrogen. The equations for the sample dilution were established, relating the measured impurity amount fractions in the sample mixture to their partial pressures in the sealed container and, in the case of oxygen, to the air pressure. Ion–molecule reaction mass spectrometry allowed identification and measurement of trace impurities corresponding to partial pressures in the range of 1 hPa in the container. The method was applied for determining the identity and amount of gaseous impurities in n-butane used in implantable gas pressure–operated drug infusion pumps. Impurities from the n-butane supply cylinder or from decomposition products, for example due to the laser welding of the Ti plugs of the containers, could be excluded by the results of saturation vapour pressure measurements, FID gas chromatograms and IMR mass spectra. The variability in pressure versus volume among tested infusion pump samples was associated with excess oxygen, attributable to an excessive residual air pressure in the gas containers before they were filled with n-butane. The sample preparation method is principally applicable to measure the composition of small amounts of gas mixtures and gaseous impurities with identified IMR mass spectra down to trace levels—even for ubiquitous substances like oxygen. The volume of the produced gas mixtures allows characterisation of the gas by standard gas analytical methods and for impurities by trace gas analytical methods.
Keywords: Liquefied pressurised gas; Infusion pump; Oxygen measurement; Quantitative mass spectrometry; Residual air; Static gas dilution; Trace gas analysis
The quality coefficient as performance assessment parameter of straight line calibration curves in relationship with the number of calibration points by Jacques O. De Beer; Caroline Naert; Eric Deconinck (pp. 265-274).
Knowledge of the response function (y = f(x)) is essential in the validation of quantitative analysis methods as it describes the mathematical relationship between measurable responses and the concentrations or quantities of the analyte in the sample within a suitable range. The most common response function used is a straight line obtained by ordinary least squares (OLS) regression. Suitability of calibration lines obtained by OLS regression might be verified by calculation of a quality coefficient (QCmean). Mathematical modelling performed previously showed that with respect to critical limit values for g, which controls the symmetry of the prediction interval of the abscissa value obtained from the confidence intervals around the OLS calibration curve, a corresponding quality coefficient value exists as a quality performance parameter which is related to the spread of the abscissa values around their mean. In this paper, new mathematical models are developed to demonstrate to which extend also the number n of calibration points (x i ,y i ) defines the required value for the quality coefficient (QCmean) for different values of g. From these models, it could be established that the attribution of a critical limit value to QCmean as a performance parameter for straight line calibration cannot be arbitrary chosen but has to rely on the mathematical model relating QCmean, the g-value, the number n of calibration points and the spread of the x i -values around their mean. Practical measures for analysts are provided which tend to lower the g-value of straight calibration lines beneath critical values and enable to improve the quality of the calibration line applied for analysis, as demonstrated in an elaborated example.
Keywords: Ordinary least squares (OLS) regression; Straight line calibration; Number of calibration points; Quality coefficient (QCmean); g-value; Performance assessment
Estimation of the standard uncertainty of a calibration curve: application to sulfur mass concentration determination in fuels by Dimitrios Theodorou; Ypatia Zannikou; Fanourios Zannikos (pp. 275-281).
The construction of a calibration curve using least square linear regression is common in many analytical measurements, and it comprises an important uncertainty component of the whole analytical procedure uncertainty. In the present work, various methodologies are applied concerning the estimation of the standard uncertainty of a calibration curve used for the determination of sulfur mass concentration in fuels. The methodologies applied include the GUM uncertainty framework, the Kragten numerical method, the Monte Carlo method (MCM) as well as the approximate equation calculating the standard error of prediction. The standard uncertainty results obtained by all methodologies agree well (0.172–0.175 ng μL−1). Aspects of inappropriate use of the approximate equation of the standard error of prediction, which leads to overestimation or underestimation of calculated uncertainty, are discussed. Moreover, the importance of the correlation between calibration curve parameters (slope and intercept) within GUM, MCM and Kragten approaches is examined.
Keywords: GUM; Monte Carlo method; Uncertainty; Calibration curve; Sulfur mass concentration; Fuel
Use of a replicated Latin square design in a homogeneity test for high purity organic melting point standards by Stephen L. R. Ellison; Nicola Grimes; Fahmina Fardus; Michael P. L. Ellison (pp. 283-290).
The use of a replicated Latin square design for reference material homogeneity assessment is illustrated by application to a homogeneity study of eight high-purity organic materials certified for melting point. The design controlled for both a three-level location effect and a run effect. Variance components were extracted using mixed effects modelling using a restricted maximum likelihood method. An alternative classical ANOVA calculation is also given. The effect of appreciable numerical rounding by the instrument software was investigated and shown to be acceptable for the particular example. Estimation of the scale of location and run effects showed that in this example the location effect was both statistically and practically significant, while the run effect was not statistically significant at the 95% level of confidence. The design allowed unbiased estimates of between-unit variances in the presence of both interfering effects.
Keywords: Certified reference material; Melting point; Homogeneity; Experimental design; Latin square
Estimating measurement uncertainty in high-performance liquid chromatography methods by Tatjana Tomić; Nada Uzorinac Nasipak; Sandra Babić (pp. 291-300).
In every measurement procedure, it is important to know the components of measurement uncertainty affecting the quality of measured result and reliability of quantified result. The procedure for recognizing measurement uncertainty is not universal but depends on the method and sample type. It has to be made according to good laboratory practice. This paper aims at showing the comparison of measurement uncertainty component estimations for three methods using the high-performance liquid chromatography techniques: determination of the type and content of aromatic hydrocarbons in diesel fuels and petroleum distillates by normal phase high-performance liquid chromatography, determination of nitrates in water samples by ion chromatography, and determination of molecular weights of polystyrene by size exclusion chromatography technique. Both similarity and differences were found during the measurement uncertainty component estimation, and conclusions about influences of certain components on the result uncertainty were made.
Keywords: Measurement uncertainty; High-performance liquid chromatography (HPLC); Ion chromatography (IC); Size exclusion chromatography (SEC)
Uncertainty budget for multi-elemental analysis of plant nutrients in conifer foliar material using inductively coupled plasma atomic emission spectrometry (ICP-AES) by K. E. Anders Ohlsson (pp. 301-313).
Measurement uncertainties evaluated according to GUM were given in an uncertainty budget for the measurement of mass fractions of 12 elements in conifer tree needle materials. The measurement was performed using ICP-AES, with prior microwave digestion of the dried sample material. The uncertainty budget for Ca as an example showed that correction for a systematic error was the main source of measurement uncertainty. The key to reduced measurement uncertainty therefore lies in identifying the main sources of systematic errors, and reducing the uncertainty associated with their correction. The usefulness of the uncertainty budget was demonstrated in its application to method validation, to the design of a quality control program, and finally for guiding method optimization.
Keywords: Metrology in chemistry; Analytical chemistry; Measurement uncertainty; Plant analysis; ICP-AES
A bilateral study for the establishment of comparability in the measurement of ethanol in bioethanol fuel using isotope dilution mass spectrometry by Tang Lin Teo; Can Quan; Pui Sze Cheow; Ting Huang; Tong Kooi Lee; Hongmei Li; Wei Zhang (pp. 315-321).
A bilateral comparative study between two metrology institutes was conducted for the determination of ethanol in bioethanol fuel by isotope dilution mass spectrometry. Measurement procedures were independently developed by the Health Sciences Authority (Singapore) and the National Institute of Metrology (People’s Republic of China). The methods used included headspace gas chromatography–high-resolution mass spectrometry, headspace gas chromatography–mass spectrometry (GC-MS) and direct injection to GC-MS. An investigation of all potential sources of uncertainty, including a component of uncertainty due to the effect of using different instruments such as gas chromatography–flame ionization detector method, commonly adopted for the analysis of organic volatiles, was carried out. The results of the analyses are consistent within the associated measurement uncertainty of each laboratory, reported at approximately 95% confidence level.
Keywords: Gas chromatography; Isotope dilution mass spectrometry; Ethanol; Bioethanol fuel
Method validation and measurement uncertainty evaluation for measurement of mass concentration of organic acids in fermentation broths by using ion chromatography by Andreja Drolc; Albin Pintar (pp. 323-330).
In the present paper, a methodology for method validation and measurement uncertainty evaluation for the measurement of mass concentration of organic acids in fermentation broths was developed. Acetic acid was selected as a representative of organic acids. A detailed procedure for in-house method validation based on simple experimental design and consistent statistics is presented. In addition, a step-by-step illustration of “Bottom-Up” approach for measurement uncertainty evaluation of acetic acid in fermentation broths is also provided. The major sources of uncertainty of the result of measurement were identified and the combined uncertainty was calculated. Our analytical protocol allowed us to quantify acetic acid in fermentation broths in mass concentrations up to 75 g L−1 with satisfactory recovery (102.3%) and repeatability lower than 2%. We also estimated within-laboratory reproducibility over 3-month period, which was 2.3%. We proved that the method was selective for the measurement of mass concentration of acetic acid in fermentation broths. Measurement uncertainty of results was evaluated to be 6.2% with 95% confidence level. After validation and measurement uncertainty evaluation steps, results obtained showed that the method can be applied to efficiently monitor fermentation processes.
Keywords: Ion chromatography; Organic acids; Method validation; Measurement uncertainty; Fermentation broths
Implementation of Good Laboratory Practices (NIT-DICLA-035, Inmetro) in a technological platforms network: the Fiocruz experience by Renata Almeida de Souza; Cassia Docena; Patricia dos Santos Silva; Ana Beatriz Moraes da Silva; Ana Paula Oliveira Brum (pp. 331-339).
The technological platforms network (TPN) of the Oswaldo Cruz Foundation was developed as the result of the need to provide technical and scientific services to the Brazilian public health and health research networks through the use of high cost, state-of-the-art, multiuser equipment. In order to improve the quality of the services offered, a quality management system (QMS) was implemented in a group of subunits of the TPN. To achieve the planned objectives, a review of all the existing guidelines was carried out first, which led to the choice of a Brazilian guideline: Inmetro NIT-DICLA-035, “Good Laboratory Practices” (GLP). The next steps were the choice of the platform subunits (Pilot Project), the drafting of relevant documentation, and the creation of a quality assurance structure as well as other activities. It was clear that a proper interpretation and understanding of GLP in these platforms could make a difference in the efficacy and effectiveness of the system defined. The expertise gained through the implementation of QMS in the Pilot Project has enabled GLP implementation in the other TPN subunit platforms.
Keywords: Quality management; Research and technological development; Technological platforms; Good laboratory practice
Implementation of a quality assurance system according to GMP and ISO 9001:2008 standard for radiopharmaceutical production in a public research centre by Michela Poli; Debora Petroni; Silvia Pardini; Piero A. Salvadori; Luca Menichetti (pp. 341-348).
The production of pharmaceuticals is one of the most highly regulated fields in terms of quality. The body of good manufacturing practice (GMP) represents the standard required by law; GMP embraces the guidelines that regulate all activities related to the production and quality control of medicinal products for human and veterinary use. This paper deals with the implementation of a quality management system (QMS) in compliance with GMP and ISO 9001 standards for the production and distribution of radiopharmaceuticals in a public research institute. The production of 2-[18F]fluoro-2-deoxy-d-glucose has been implemented according to GMP standards and has been licensed by the national Authority in 2007. In 2010, a project to orient the system’s GMP compliance to ISO 9001 standards has been approved. A QMS conforming to ISO 9001:2008 should be considered an important additional step in terms of quality, because ISO 9001 also takes into account economic and financial aspects, design and development aspects and introduces management review for measurement and analysis of the process with the aim of improving performances. The harmonization between GMP and ISO has been defined following the Pharmaceutical Quality System Q10 guideline developed by International Conference on Harmonization.
Keywords: GMP; Quality assurance; Radiopharmaceutical; ISO 9001:2008; 18F-FDG; ICH Q10
Ordinal quantities in clinical laboratory sciences by Xavier Fuentes-Arderiu (pp. 349-351).
From an ontological point of view, the concept ‘property’ may be defined as “that which when possessed by an object contributes to it being as it is”. Ordinal quantity is one of the types into which properties may be divided. Ordinal quantity is understood internationally as a “quantity defined by a conventional measurement procedure, for which a total ordering relation can be established, according to magnitude, with other quantities of the same kind, but for which no algebraic operations among those quantities exist”. The term ordinal quantity may be preceded by an adjective (generic, subgeneric, specific, or individual) to clarify the relation object–property. Ordinal quantities may have values belonging to binary ordinal scales and polinay ordinal scales.
Keywords: Metrology; Ordinal quantity; Ordinal property; Ordinal scale; Binary scale; Polinary scale
Traceability in perspective by Michael Thompson (pp. 353-354).
Results that reference SI units rarely pose problems in chemical measurement because traceable standards, with uncertainties derived from a chain of calibrations from the SI, are readily available at the analyst’s bench. These uncertainties are nearly always far smaller than that required for fitness for purpose in the analytical result. Moreover, the greater part of the uncertainty in a typical result is not derived from primary measurements traceable to the SI but from recovery problems and matrix effects. Even so, the incidence of wildly inaccurate results stems not from this uncertainty but from “blunders”, deviations from the correct procedure. Attention to traceability beyond that employed by any competent analyst therefore cannot reduce the uncertainty. Furthermore, there is no rational reason to reduce the uncertainty if the result is already fit for purpose. The current focus on traceability is distracting analysts from the more pressing task of eliminating blunders.
Keywords: Traceability; Uncertainty; Fitness for purpose; Blunders