Accreditation and Quality Assurance 

About: Accreditation and Quality Assurance is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Measurement uncertainty & Accreditation. It has an ISSN identifier of 0949-1775. Over the lifetime, 2055 publications have been published receiving 16645 citations. The journal is also known as: Accreditation and quality assurance (Print).

Reference materials for large-scale metal deposition surveys

Abstract: In order to ensure quality assurance in large-scale environmental contamination studies involving many different analytical laboratories, the use of calibrated reference materials is essential. Prior to a survey of atmospheric metal deposition in 1995 comprising 20 countries and covering large parts of Europe, the lack of suitable reference materials of moss and organic-rich soil was apparent. In order to improve the quality of analytical data to be produced in this international survey, candidate analytical laboratories were invited to participate in an intercomparison exercise. Three moss and three soil humus reference samples specifically prepared for this purpose were distributed anonymously among the laboratories, which were asked to report data for ten priority elements (V, Cr, Fe, Ni, Cu, Zn, As, Cd, Hg, Pb) and as many additional elements as they determined normally. In this paper the analytical data from the intercomparison are evaluated, and recommended values for the ten priority elements and 17 additional elements (B, Na, Mg, Al, S, K, Ca, Mn, Co, Se, Rb, Sr, Sb, Cs, Ba, La, Th) in each of the six reference samples are established. These samples should be useful for similar future studies including areas where the contamination levels are very low.

Homogeneity and stability of reference materials

Abstract: Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation to create materials as homogeneous and stable as possible. Degradation can generally be minimised by reducing the water activity of the material to a level between 0.15 and 0.35. However, careful preparation by itself is not enough. Positive demonstration of homogeneity and stability is required from the perspective of implementing uncertainty calculus according to the Guide to the Expression of Uncertainty in Measurement (GUM). In many cases, homogeneity and stability studies fail to give sufficient quantitative information on homogeneity and stability, mainly because of a lack of measurement repeatability and insufficient number of replicates. In this work, some solutions to these problems and their implications are presented.

Understanding the meaning of accuracy, trueness and precision

Abstract: Clear definitions of basic terms, used to describe the quality of measurements, is essential for communication among scientists as well as when reporting measurement results to clients. Even if appropriate definitions are given in international standards and guidelines, the understanding of some basic terms sometimes proves difficult. The reasons for this are various, e.g., the same words being defined rather differently in encyclopaedias and in international standards as well as concepts, well established in some languages, that may be relatively new in other national communities and at large in the international one. Here we present a matrix intended to clarify the relationships between the type of error affecting an analytical measurement, the respective qualitative concepts (performance characteristics) and their quantitative expression.

Linearity of calibration curves: use and misuse of the correlation coefficient

Abstract: The correlation coefficient is commonly used to evaluate the de- gree of linear association between two variables. However, it can be shown that a correlation coefficient very close to one might also be ob- tained for a clear curved relation- ship. Other statistical tests, like the Lack-of-fit and Mandel's fitting test thus appear more suitable for the validation of the linear calibration model. A number of cadmium cali- bration curves from atomic absorp- tion spectroscopy were assessed for their linearity. All the investigated calibration curves were characterized by a high correlation coefficient (r >0.997) and low quality coeffi- cient (QC <5%), but the straight-line model was systematically rejected at the 95% confidence level on the ba- sis of the Lack-of-fit and Mandel's fitting test. Furthermore, significant- ly different results were achieved be- tween a linear regression model (LRM) and a quadratic regression (QRM) model in forecasting values for mid-scale calibration standards. The results obtained with the QRM did not differ significantly from the theoretically expected value, while those obtained with the LRM were systematically biased. It was con- cluded that a straight-line model with a high correlation coefficient, but with a lack-of-fit, yields signifi- cantly less accurate results than its curvilinear alternative.

Bioanalytical method validation and its implications for forensic and clinical toxicology – A review

Abstract: The reliability of analytical data is very important to forensic and clinical toxicologists for the correct interpretation of toxicological findings This makes (bio)analytical method validation an integral part of quality management and accreditation in analytical toxicology Therefore, consensus should be reached in this field on the kind and extent of validation experiments as well as on acceptance criteria for validation parameters In this review, the most important papers published on this topic since 1991 have been reviewed Terminology, theoretical and practical aspects as well as implications for forensic and clinical toxicology of the following validation parameters are discussed: selectivity (specificity), calibration model (linearity), accuracy, precision, limits, stability, recovery and ruggedness (robustness)