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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.7, #10)


Organic coffee discrimination with INAA and data mining/KDD techniques: new perspectives for coffee trade by Elisabete A. De Nadai Fernandes; Fábio S. Tagliaferro; Adriano Azevedo-Filho; Peter Bode (pp. 378-387).
Samples of green coffee (Coffea arabica) produced in the crop year 1999/2000 in Minas Gerais state, Brazil, were analyzed for the elements Al, Ba, Br, Ca, Cl, Co, Cs, Cu, Fe, K, Mg, Mn, Na, Rb, S, Sc, and Zn using instrumental neutron activation analysis (INAA), in an attempt to establish fingerprints of organically grown coffee. Using data mining/KDD techniques the elements Br, Ca, Cs, Co, Mn, and Rb were found to be suited as markers for discrimination of organic from conventional coffees.

Keywords: Keywords Organic coffee; Inorganic composition; Discrimination methods; Pattern recognition; Quality demonstration vs. quality designation; Data mining; KDD


Compliance with legal requirements: definition of limits, sampling and measurement uncertainty by Hermann Glaeser (pp. 388-391).
In many cases compositional requirements for foodstuffs (e.g. limits for the fat, protein, dry matter, or water content) are established by legislation. Adequate compliance testing is possible only if limits are clearly defined, taking measurement and sampling uncertainty into consideration. Furthermore, decisions on compliance must be based on samples which reflect the composition of the quantity to be evaluated. The resulting sample sizes are normally regarded by food inspection authorities as being much larger than acceptable. Consequently, an alternative strategy should be developed. Autocontrol data (i.e. inspection results obtained by the factory) in principle provide an adequate data basis for decisions on compliance. However, they must be reliable and the food inspection authority must have access to these data on request. Using these data and on condition that they show an approximate normal distribution, an inspection strategy based on arithmetic mean and standard deviation can be developed. Reliable and transparent decisions on compliance can thus be made. In many cases an adequate verification of food authenticity requires a comparison of raw material and product composition. Maximum acceptable differences, taking the relevant sources of variation into consideration, have to be defined and should be used instead of limits.

Keywords: Keywords Foodstuffs; Compliance testing; Definition of limits; Measurement error; Sampling error; Autocontrol; Authenticity


Reliability of food measurements: the application of proficiency testing to GMO analysis by J. Powell; Linda Owen (pp. 392-402).
This paper reviews the experience of the Food Analysis Performance Assessment Scheme (FAPAS®) in operating a proficiency testing scheme for the analysis of genetically modified (GM) food. Initial rounds of proficiency testing have shown a tendency for laboratories to over-estimate GM levels, results obtained by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) detection methods to be significantly different and that data are skewed and not normally distributed until log-transformed. During the initial rounds, it was found that for analysis and quantification of GM material, it was not possible to assign a target value for standard deviation external to the round data, from which performance could be assessed. However, when working in a log scale, the internally derived, robust standard deviation (^σ) was found to be constant and could be used directly to predict a target value (σ) for performance assessment. Results from the first four rounds have provided valuable information and a general overview of laboratory ability. Choosing a target value for standard deviation which reflects current best practice has enabled laboratory performance to be assessed. Issues surrounding the assessment of performance are discussed which highlight some of the implications raised as a result of this initial assessment, regarding the enforcement of European labelling legislation.

Keywords: Keywords Proficiency testing; GMO analysis; FAPAS®; GeMMA; Target standard deviation; z-score; Threshold


Comparison of strategies to quantify uncertainty of lead measurements in biological tissue at mg kg–1 level by M. Feinberg; Michel Montamat; Cédric Rivier; Béatrice Lalère; Guillaume Labarraque (pp. 403-408).
The expression of measurement uncertainty in analytical chemistry still presents some difficulties. According to the various guides and standards, several approaches are possible. This paper present two referenced approaches applied to the determination of Pb in a biological tissue at the mg kg–1 level. Estimations were achieved, either from inter-laboratory precision data, or from the uncertainty propagation equation applied to the measurements of a single laboratory. When comparing final values, for an average concentration of about 2.0 mg kg–1, expanded uncertainties range from ±0.05 mg kg–1 up to ±0.31 mg kg–1, i.e. by a factor of 6. Obviously, both approaches of estimating uncertainty do not cover the same sources of uncertainty and it is interesting to try to understand better these discrepancies in order to try to define realistic guidelines for analysts. Moreover the experimental results of the study are given where a wide number of techniques is applied.

Keywords: Keywords Uncertainty; Trace elements; Reference material certification


Reliability of food measurements – a South African perspective by Louwrens Erasmus Smit (pp. 409-411).
 High quality analysis of food involves a comprehensive process, which includes proper sampling, validated methodology, experienced technical staff and the use of standard reference materials. Today there is more international emphasis not only on generating food composition data but also on data quality and the main issue is that South African data should be internationally recognized as acceptable and representative. Quality is multi-dimensional and should at least include aspects of accuracy, precision and representativeness. A major step forward is that laboratories can apply for accreditation, which involves, inter alia, documented, validated methodology, regular interlaboratory studies, the use of certified reference materials and the existence of a sound quality system. The South African National Accreditation System (SANAS) is a regulatory body in South Africa, which is internationally recognized. Assessment of laboratories against specific standards is performed regularly and laboratories have to comply with certain managerial and technical requirements. Once a laboratory is accredited, ongoing validation and verification of results as well as regular assessment ensure reliability of results and overall competency of the laboratory. With a quality assurance programme in place, the reliability of results of the Irene laboratory is beyond doubt and nutrient data could be included in food composition tables.

Keywords: Keywords Measurement accuracy; Accreditation; Reliability; Food composition data


Influence of buffer quality on pH measurement uncertainty: prediction and experimental evaluation by Irina Ekeltchik; Elena Kardash-Strochkova; Orna Dreazen; I. Kuselman (pp. 412-416).
Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH (e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties of the experimental results are close to the predicted ones obtained by the simulation.

Keywords: Keywords  Measurement uncertainty; pH; Monte Carlo method; Calibration; Buffers


Reference procedures for testing and chemical analysis provided by BAM by Werner Hässelbarth (pp. 418-419).
Recently the German Federal Institute for Materials Research and Testing (BAM) has made an inventory of the reference procedures for testing and chemical analysis provided by its laboratories. This compilation was first published as a printed catalogue [1] but is now also available on the Internet at the BAM website (see http://www.bam.de/service, direct link: http://www.bam.de/ reference_procedures.htm).The intention of this article is to give an introduction to the catalogue and provide relevant background information.

Keywords: Keywords Reference procedures; Reference methods; Reference values; Traceability; Validation


A participatory improvement activity of the EC-JRC to improve metrology in chemistry in EU candidate countries by N. Majcen; E. Bulska; I. Leito; Emilia Vassileva; Ioannis Papadakis; Philip Taylor (pp. 419-422).
In 2000, the European Commission-Joint Research Centre, Institute for Reference Materials and Measurements (EC-JRC-IRMM) set up a project to improve the scientific basis for metrology in chemistry (MiC) in EU candidate countries. Several activities were initiated (training, fellowships, sponsoring seminars, conferences and participation in the International Measurement Evaluation Programme – IMEP). A particular initiative, discussed here, was to assist each of the national measurement institutes of these countries to write a status report on MiC. Most importantly, the report was intended to be the end-product of a process to document the current status of MiC. Intentionally, this process involved not only the providers of services in MiC but all the major stakeholders in this activity (e.g. major field laboratories, accreditation bodies, regulatory bodies, educators, professional bodies). The status reports are intended to be the first step of the future improvement process. In those countries where writing of the status reports has been started (Slovenia, Poland, Bulgaria and Estonia) the first signs are that this process leads to better co-operation and particularly a better understanding of what the future role and activities of each of these stakeholders should be.

Keywords: Keywords  Metrology in chemistry; Metrological infrastructure; Status report
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