Review of European Union requirements: quality standards for food analysis laboratories

 The European Union has prescribed strict quality standards for official food laboratories and the methods of analysis to be used in laboratories when carrying out official food control work. These requirements, which are based on accreditation, participation in proficiency testing schemes and using validated methods of analysis, are described in detail. The similar approach being taken within the Codex Alimentarius Commission is also outlined. The procedures prescribed will ensure that official food control laboratories have in place the measures to ensure that consistently reliable data can be produced. Received: 29 November 1995 Accepted: 8 January 1996     

Quality issues in proficiency testing

 Proficiency testing is a means of assessing the ability of laboratories to competently perform specific tests and/or measurements. It supplements a laboratory's own internal quality control procedure by providing an additional external audit of their testing capability and provides laboratories with a sound basis for continuous improvement. It is also a means towards achieving comparability of measurement between laboratories. Participation is one of the few ways in which a laboratory can compare its performance with that of other laboratories. Good performance in proficiency testing schemes provides independent evidence and hence reassurance to the laboratory and its clients that its procedures, test methods and other laboratory operations are under control. For test results to have any credibility, they must be traceable to a standard of measurement, preferably in terms of SI units, and must be accompanied by a statement of uncertainty. Analytical chemists are coming to realise that this is just as true in their field as it is for physical measurements, and applies equally to proficiency testing results and laboratory test reports. Recent approaches toward ensuring the quality and comparability of proficiency testing schemes and the means of evaluating proficiency test results are described. These have led to the drafting of guidelines and subsequently to the development of international requirements for the competence of scheme providers. Received: 2 January 1999 · Accepted: 7 April 1999     

Proficiency testing schemes for therapeutics and toxicology

 This report addresses the proposition: current proficiency testing (PT) schemes for therapeutics and toxicology can easily engender complacency. The proposition was based on the premise that there are substantial between-laboratory differences and objectives in the supply of services for the measurement of drugs, as a result of which it is difficult to design PT schemes which adequately cover the requirements of all laboratories. Thus, acceptable performance in a PT scheme may lead participants to consider that they have tested their procedures more rigorously than is the case. Four areas, validity of the PT scheme, PT material, frequency of testing and acceptance criteria are examined. Received: 15 April 2000 · Accepted: 15 April 2000     

Quality assurance in forensic science: the UK situation

 The contribution to the debate on the quality of forensic science in the UK by various bodies including government, professional and accreditation organisations, is discussed. The practical steps that have been taken over many years to improve quality and to ensure that there are well-documented systems in place are considered. These include laboratory quality systems, proficiency testing and the training of forensic scientists. Received: 6 November 1996 Accepted: 12 December 1996     

Integration of metrological principles and performance evaluation in a proficiency testing scheme in support of the Council Directive 98/83/EC

Proficiency testing as a means of external quality assessment plays the role of independent evidence of laboratories’ performance. To enable laboratories to fulfil the requirements stated in legislation, methodology for evaluation of laboratories’ performance in proficiency testing schemes should incorporate principles of measurement results which are fit for intended use and incorporate evaluation of laboratories’ performances based on independent reference value. A proficiency testing scheme was designed to support Drinking Water Directive (98/83/EC) specifically. The methodology for performance evaluation, which takes into account a “fitness for purpose”-based standard deviation for proficiency assessment, is proposed and discussed in terms of requirements of the Drinking Water Directive. A ζ′-score, modified by application of target uncertainty was developed in a way that fulfils requirements defined in the legislation. As an illustration, results are reported for nitrate concentration in water. The approach presented can also be applied to other fields of measurements.     

Harmonization and transferability of performance assessment: experience from four serum aluminum proficiency testing schemes

Proficiency testing schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. Where several schemes operate in the same analytical sector, there are risks that assessments of performance may be in conflict. Performance assessment for the determination of trace elements such as aluminum in serum is particularly important due to the high risk of contamination and therefore erroneous results. The objectives of this work were (1) to compare several mathematical models to establish a predefined standard deviation for proficiency assessment and (2) to evaluate the influence of instrumental methods and proficiency testing scheme on the assessment of performance for serum aluminum measurements. For this purpose, three samples were sent to the participants of four proficiency testing schemes. Assigned values were calculated according to algorithm A according to ISO 13528 and standard deviation for proficiency assessment according to three methods based on individual variability, state of the art or previous proficiency testing results. The method based on individual variability produced a more stringent standard deviation compared to analytical imprecision based on the state of the art. The instrumental methods gave similar results, whereas significant differences were observed between the four proficiency testing schemes indicating that harmonization of the standard deviation for proficiency assessment fails to allow transferability from one proficiency testing scheme to another and that additional factor(s) contribute to variability in performance assessment.     

Implementation of proficiency testing schemes for a limited number of participants

A metrological background for the selection and use of proficiency testing (PT) schemes for a limited number N of laboratories-participants (less than 20–30) is discussed. The following basic scenarios are taken into account: (1) adequate matrix certified reference materials (CRM) or in-house reference materials (IHRM) with traceable property values are available for PT use as test items; (2) no appropriate matrix CRM is available, but a CRM or IHRM with traceable property values can be applied as a spike or similar; (3) only an IHRM with limited traceability is available. The discussion also considers the effect of a limited population of PT participants N _p on statistical assessment of the PT results for a given sample of N responses from this population. When N _p is finite and the sample fraction N/N _p is not negligible, a correction to the statistical parameters may be necessary. Scores suitable for laboratory performance assessment in such PT schemes are compared. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.     

Why do food analysts need quality assurance?

 Most sophisticated products require testing for compliance with specifications and safety regulations before release into many markets, and trade in many simpler commodities and products also requires supporting technical information. Test documentation has become an essential element in this trade. Food intended for human consumption certainly falls into the "sophisticated products" category. Lack of acceptance of laboratory test data across national borders may be a significant barrier to trade. In order to avoid such barriers and unnecessary duplication of laboratory tests, mutual recognition of laboratory results should be regarded as an important means of facilitating international trade in food products. It is difficult to envisage recognition of test data across borders without internationally agreed criteria for assessing the competence of testing. These criteria should, as a minimum, require that a laboratory involved in the analysis of foods operates a suitable quality system. The laboratory must create a quality system appropriate to the type, range and volume of work performed. It is necessary for the elements of this system to be documented in a quality manual which is available for use by the laboratory personnel. The quality manual must be kept up-to-date by a person or persons having responsibility for quality assurance within the laboratory. This paper describes and discusses the elements of a quality system in a food laboratory, including suitable quality assurance measures, the use of validated analytical methods and participation in proficiency testing schemes. Received: 24 February 1996 Accepted: 13 March 1996     

Key metrological issues in proficiency testing––response to “Metrological compatibility-a key issue in further accreditation” by K. Heydorn

A discussion of proficiency testing (PT) topics started by Heydorn (Accred Qual Assur 15:643–645, 2010) is continued in the present paper. The role of PT in the accreditation of testing/analytical laboratories, the use of consensus values (average or weighted average, median, observed standard deviation, etc.) and a metrological background of PT schemes are discussed. It is shown that metrological traceability, comparability, and compatibility, as well as commutability of a reference material, are the key issues of any PT scheme that applies certified reference material as test items. Metrological compatibility of PT results in such schemes is a property demonstrating the closeness of the PT results to the certified value in comparison with the measurement uncertainty of their difference. The metrological background is especially important for the selection and use of PT schemes for a limited number of participants (fewer than 30) as detailed in IUPAC/CITAC Guide on the topic published in 2010 in Pure Appl Chem 82(5):1099–1135.     

Statistical analysis of serum protein electrophoresis results in External Quality Assessment schemes

The goal of External Quality Assessment (EQA) schemes is to ensure that results obtained on a particular specimen in a given clinical laboratory are compatible with those obtained by other laboratories on the same specimen. Serum protein electrophoresis is a laboratory test consisting of five fractions (albumin, α₁, α₂, β and γ globulins), which sum up to 100% of total proteins. So far, in EQA schemes the five fractions have been analyzed separately as for ordinary tests like glucose or cholesterol. This approach does not consider the fractions as a whole and the linear relationship between them. A statistical approach has been developed to analyze EQA electrophoresis results from a global standpoint by using robust multivariate method to eliminate the effect of outlying profiles. As illustrated on electrophoretic data from the Belgian EQA scheme, the novel approach improves the detection of poor performing laboratories. The method will be implemented in the Belgian EQA scheme on a routine basis.     

Metrological traceability is not always a straight line

The two most important concepts in metrology are certainly “traceability to standards” and “measurement uncertainty evaluation”. So far the questions related to these concepts have been reasonably solved in the metrology of “classical quantities”, but for the introduction of metrological concepts in new fields, such as chemistry and biology, a lot of problems remain and must be solved in order to support international arrangements. In this presentation, the authors want to develop the strategy implemented at Laboratoire national de métrologie et d’essais (LNE) in metrology in chemistry and biology. The strategy is based on: (1) pure solutions for calibration of analytical instruments, (2) use of certified reference materials (matrix reference materials), and (3) participation to proficiency testing schemes. Examples will be presented in organic and inorganic chemistry. For laboratory medicine, proficiency testing providers play an important role in the organization of External Quality Assessment Schemes. For the time being, the reference value or the assigned value of the comparison is calculated with the results obtained by the participants. This assigned value is not often traceable to SI units. One of the methods suggested by LNE is to ensure the metrological traceability to SI units of the assigned value for the more critical quantities carried on analytes by implementing the Joint committee for traceability in laboratory medicine reference methods.     

The determination of an accepted reference value from proficiency data with stated uncertainties

Proficiency data with stated uncertainties represent a unique opportunity for testing that the reported uncertainties are consistent with the Guide to the expression of uncertainty in measurement (GUM). In most proficiency tests, however, this opportunity is forfeited, because proficiency data are processed without regard to their uncertainties. In this paper we present alternative approaches for determining a reference value as the weighted mean of all mutually consistent results and their stated uncertainties. Using an accepted reference value each reported uncertainty estimate can be expressed as an E _n number, but a value of confirms its validity only if the uncertainty of the reference value is negligible in comparison.Reference values calculated for results from an International Measurement Evaluation Programme (IMEP-9) by “bottom up” as well as “top down” methods were practically identical, although the first strategy yielded the lowest uncertainty. A plot of individual coefficients of variation (CV) versus E _n numbers helps interpretation of the proficiency data, which could be used to validate relative uncertainties down to <1%.     

Accreditation of PT providers – is it worth the money?

This topic is being presented from two perspectives, namely the views of an accreditation body and those of an accredited provider of external quality assessment schemes. The first perspective, from an accreditation body, is based on the experience of Australia's national laboratory accreditation body (NATA), which has accredited fourteen proficiency testing (PT) providers and is currently processing an application from another. The second perspective is based on the experience of EQUALIS, the national quality assurance organisation for laboratory medicine in Sweden, which was granted accreditation in 2002.Presented at 5^th Eurachem Workshop on Proficiency testing in analytical chemistry, microbiology and laboratory medicine, Portorož (Slovenia) 25–27 Sept 2005     

External quality assessment schemes for clinical laboratories

 The clinical routine laboratory generally utilizes cheap, easy and rapid measurement procedures ("methods") in order to meet the requirement for the production of many analytical results (500–3000 per day) of hundreds of different types. The measurement procedures are optimized for the analysis of native patients' samples, but are frequently sensitive to deviation of the composition of the matrix from that in normal fresh samples. The inherent lack of stability of patient samples means that control samples need to be stabilized. The method of stabilization is critical. Furthermore, the method of "spiking" samples with pathological material is a matter of concern. Generally, minimally processed patients' samples should be used in external quality assessment (EQA) schemes. Consensus values are currently the most popular for use as a guide to the best results from participating laboratories in EQA schemes; these often work fairly well. However, the uncertainty and traceability of this type of value is unknown, and in some cases may even be misleading, tending to preserve bad routine methods when these are dominant in the participating laboratories. Reference measurement procedure (RMP) values are recommended to provide scientifically based information, to facilitate the proper choice of methods in the routine laboratories, and to validate the suitability of control materials in EQA schemes. The present paper provides selected examples from a study comparing consensus values with RMP values on lyophilized sera, and also presents results on a fresh frozen thawed serum for the study of commutability. Received: 8 November 1995 Accepted: 8 May 1996     

Performance of uncertainty evaluation strategies in a food proficiency scheme

A study of the performance of different uncertainty evaluation strategies among 163 voluntary respondents from food proficiency schemes is presented. Strategies included use of: single-laboratory validation data, quality control data, past proficiency testing data, reproducibility data, a measurement equation and the dispersion of replicate observations on the test material. Most performed reasonably well, but the dispersion of replicate observations underestimated uncertainty by a factor of approximately 3. Intended compliance with accreditation requirements was associated with significantly improved uncertainty evaluation performance, while intended compliance with the ISO “Guide to the expression of uncertainty in measurement” had no significant effect. Substituting estimates based on the Horwitz or Horwitz–Thompson models or on PT target standard deviation for the respondents’ own estimates of uncertainty led to a marked reduction in poor zeta scores and significant improvement in dispersion of zeta scores.     

Proficiency testing on the analytical control of precious metal production

Our experience of executing proficiency testing programs on the analysis of precious metals and precious metal bearing materials is summarized. Six proficiency testing programs of the ”distributed sample testing” type were carried out using samples essentially distinct from each other: (I) certified samples of fine gold and fine silver, and (II) recoverable raw (scrap and catalyst waste) containing precious metals of unknown contents. The test results were assessed using the London Bullion Market Association (LBMA) rules and by Z-criteria using the ISO/IEC Guide 43 scale. Satisfactory results were presented by all participants for the analysis of certified samples of fine gold and fine silver. The results of catalyst waste analysis agreed rather well, whereas the scrap analysis revealed an essential discrepancy in the data for some samples. The reasons for such discrepancies are discussed. Received: 9 June 2000 Accepted: 21 November 2000     

From GUM to alternative methods for measurement uncertainty evaluation

Since the advent of the Guide to the expression of Uncertainty in Measurement (GUM) in 1995 laying the principles of uncertainty evaluation numerous projects have been carried out to develop alternative practical methods that are easier to implement namely when it is impossible to model the measurement process for technical or economical aspects. In this paper, the author presents the recent evolution of measurement uncertainty evaluation methods. The evaluation of measurement uncertainty can be presented according to two axes based on intralaboratory and interlaboratory approaches. The intralaboratory approach includes “the modelling approach” (application of the procedure described in section 8 of the GUM, known as GUM uncertainty framework) and “the single laboratory validation approach”. The interlaboratory approaches are based on collaborative studies and they are respectively named “interlaboratory validation approach” and “proficiency testing approach”.     

The equivalence of bond-energy schemes and the determination of resonance energies

 It is argued that the preservation of algebraic equivalence between the Allen and Laidler bond-energy schemes for nonconjugated alkenes logically determines that the Allen scheme should apply to a classical structure of a conjugated hydrocarbon exactly as it stands, i.e. no additional parameters are needed. Extending the requirement of equivalence to conjugated alkenes implies that, in the Laidler scheme, the bond energy of the pure single CC bond in a conjugated system is a combination of the bond-energies of the semiconjugated and normal CC single bonds: E(C_d—C_d)=2E(C_d—C)−E(C—C). This result is a deduction and is not an independent hypothesis. The equivalence of the two schemes for conjugated hydrocarbons is demonstrated numerically, by calculating the resonance energies of some selected molecules by both methods. Received: 5 December 1999 / Accepted: 5 March 2000 / Published online: 5 June 2000     

Proficiency testing in the light of a new rationale in metrology

The novel proposed definition of measurement result in the international metrology vocabulary requires a revision of standards and guidelines for proficiency testing (PT), and a new approach to processing proficiency data is needed to test the ability of laboratories to present not only unbiased quantity values, but reliable estimates of their uncertainty. Hence, an accepted reference value with the smallest possible uncertainty is needed to ascertain the proficiency of laboratories reporting results with lower than average uncertainty. A strategy based on the T-statistic is proposed leading to an accepted reference value that fully reflects the uncertainties reported by participants in a PT scheme and permits calculation of E _n numbers to distinguish whether or not measurement results are consistent with the accepted definition of the measurand. The strategy is applied to PT data from a recent international laboratory intercomparison of uranium isotopic ratios.     

Experience with in-house PT-schemes in the chemical industry

There are many different means of demonstrating the quality of performance of an analytical laboratory. Proficiency testing (PT) is just one! As in other analytical fields, interlaboratory comparisons play an important role in the chemical industry. Collaborative trials or method performance studies do have a long tradition in this field. Sometimes they were designed as laboratory performance studies with the clear aim of making analytical results comparable, e.g. petrol, coal, gas, noble metals analyses – not to mention the biggest PT scheme run on a daily world-wide basis – trade itself. All this is an ongoing process, which started long before the idea of assessing and accrediting the performance of analytical laboratories was born. However, when striving for accreditation in 1996, the analytical production laboratories of the Chemicals Business Unit of the Bayer AG in Germany implemented another facet of PT schemes. In-house-PT schemes are performed regularly and turned out to be useful in evaluating, monitoring, and thus improving, the quality of routine analytical work. Received: 5 December 2000 Accepted: 15 January 2001