Evaluation of measurement uncertainty for analytical procedures using a linear calibration function

In the EURACHEM/CITAC draft ”Quantifying uncertainty in analytical measurement” estimations of measurement uncertainty in analytical results for linear calibration are given. In this work these estimations are compared, i.e. the uncertainty deduced from repeated observations of the sample vs. the uncertainty deduced from the standard residual deviation of the regression. As a result of this study it is shown that an uncertainty estimation based on repeated observations can give more realistic values if the condition of variance homogeneity is not correctly fulfilled in the calibration range. The complete calculation of measurement uncertainty including assessment of trueness is represented by an example concerning the determination of zinc in sediment samples using ICP-atomic emission spectrometry. Received: 9 February 2002 Accepted: 17 April 2002     

Global comparability of analytical results

 Global decisions made on the basis of chemical analytical results need global comparability. The concept of traceability is important and necessary but not sufficient to achieve global comparability, especially for routine analysis in environmental protection, health care and public safety. Sometimes comparability is only determined by the method. In this case validated methods have to be known and recognized internationally. In addition, a minimum level of proficiency of the personnel producing analytical results has to be guaranteed. Finally, a system of measures designed to build up trust is needed for worldwide acceptance of analytical results. The method of self-declaration by the supplier of chemical analytical services has the advantage of presenting specific responsibility and gaining a good reputation. Additional methods should be employed. The evaluation of reference materials by specific quality criteria is mentioned as an example. Received: 1 July 1998 · Accepted: 20 July 1998     

The evaluation of measurement uncertainty from method validation studies

 A protocol has been developed illustrating the link between validation experiments, such as precision, trueness and ruggedness testing, and measurement uncertainty evaluation. By planning validation experiments with uncertainty estimation in mind, uncertainty budgets can be obtained from validation data with little additional effort. The main stages in the uncertainty estimation process are described, and the use of trueness and ruggedness studies is discussed in detail. The practical application of the protocol will be illustrated in Part 2, with reference to a method for the determination of three markers (CI solvent red 24, quinizarin and CI solvent yellow 124) in fuel oil samples. Received: 10 April 1999 / Accepted: 24 September 1999     

A comprehensive approach to method validation based on object technology

 Method validation procedure requires a strategy for collecting those validation data that are best adapted to the analytical technique used. A flexible and general approach based on Object Linking and Embedding technology is proposed. It allows a traceable validation strategy using modular objects which encapsulate documentation, analytical data and processing logic. The contents of these objects are accessible through a standard user interface. This paper demonstrates how this can reduce experiment time, simplify evaluation efforts, and increase the ease of use of validation figures of merit. An illustration using Microsoft Visual Basic for Applications is presented, and some specific aspects are described. It consists of the evaluation of a time domain NMR technique for determining the moisture content of foods involving a multivariate calibration step. This study also illustrates how guidelines such as Good Validation Practices could be defined to present all validation documents in a standardised manner. Received: 3 September 1996 Accepted: 14 October 1996     

The evaluation of measurement uncertainty from method validation studies

 A protocol has been developed illustrating the link between validation experiments and measurement uncertainty evaluation. The application of the protocol is illustrated with reference to a method for the determination of three markers (CI solvent red 24, quinizarin and CI solvent yellow 124) in fuel oil samples. The method requires the extraction of the markers from the sample matrix by solid phase extraction followed by quantification by high performance liquid chromatography (HPLC) with diode array detection. The uncertainties for the determination of the markers were evaluated using data from precision and trueness studies using representative sample matrices spiked at a range of concentrations, and from ruggedness studies of the extraction and HPLC stages. Received: 10 April 1999 · Accepted: 24 September 1999     

Statistical evaluation of stability data for assessing variability of an analytical method

 Stability assay results of a stable solid oral dosage form, designated Product X 5 mg, were subjected to a statistical analysis in view of evaluating the intra-team repeatability and the interval-to-interval reproducibility of the analytical method. Analysis of variance and analysis of method capability were performed on stability data obtained from tablets stored in four different packages over a two-year period. Replicate-to-replicate and period-to-period standard deviations of assay results of the active drug ingredient were found to vary among the packages and were up to 1.3 and 1.5% (% assay), thus leading to maximum differences between any two reported average results of up 4.7%. Analysis of method capability showed that up to 51% of the specification range (90–110%) is taken up by variations of the reported average stability results. This large but realistic method variability does not reflect the formation of low-level impurities (ca. 0.1%) required by regulatory agencies. Received: 10 December 1998 · Accepted: 25 January 1999     

Problems of validation of computerised instruments for accredited chemical laboratories

 Some problems of validation of computerised instruments are reviewed briefly, taking essential standards and guides into account. The significant role of certified standard reference materials is underlined. An attitude of suppliers towards the validation of instruments is presented, and producers' responsibilities and obligations are discussed. The "black-box" concept is recommended as a preliminary step for the validation of computerised instruments. Two examples for gel permeation chromatography are given that illustrate a bad manufacturer's practice (BMP) and good manufacturer's practice (GMP). In the case of BMP, a need is expressed for a guide and for regulations that should be implemented into the quality assurance system. It has been proposed that the EURACHEM/VAM draft of guidance for qualification/validation of instruments should be amended by incorporating the "black-box" approach as a preliminary procedure for validation of computerised instruments, a retrospective validation procedure if the need for current validation was not foreseen or not specified, and a procedure (or selection rules) for qualification of the supplier. Moreover, the mechanisms of inspection to control the observance of the standardised rules and commonly recognised recommendations should also be considered by international quality organisations. Received: 19 November 1996 · Accepted: 20 March 1997     

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

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). Received: 16 June 2002 Accepted: 12 July 2002 Part of this review was published in the communications of the International Association of Forensic Toxicologists (TIAFT; TIAFT Bulletin 32 (2002): 16–23) and of the Society for Forensic and Toxicologic Chemistry (GTFCH; Toxichem and Krimitech 68 (2001): 116-126). Correspondence to F. T. Peters     

The rational use of proficiency tests and intercomparisons

 Interlaboratory comparisons (in the following abbreviated as intercomparisons) regarding tests, analyses or measurements are among the most worthwhile measures a laboratory can take in order to confirm that its services to clients include the provision of correct results within a stated uncertainty. They give a picture of the whole performance of the laboratory, and they should be used much more than at present. Unfortunately such intercomparisons are, and are made, expensive and prestigious by the formalisms employed in many cases. The connection between intercomparisons and proficiency tests and their use for different purposes is briefly discussed. Some suggestions are made on how to improve the present state of the art, i.e. how to increase the use of intercomparisons, how to perform them efficiently and how to make optimal use of the results. Received: 6 December 1997 · Accepted: 30 January 1998     

Uncertainty profiles for the validation of analytical methods

This article aims to expose a new global strategy for the validation of analytical methods and the estimation of measurement uncertainty. Our purpose is to allow to researchers in the field of analytical chemistry get access to a powerful tool for the evaluation of quantitative analytical procedures. Indeed, the proposed strategy facilitates analytical validation by providing a decision tool based on the uncertainty profile and the β-content tolerance interval. Equally important, this approach allows a good estimate of measurement uncertainty by using data validation and without recourse to other additional experiments.In the example below, we confirmed the applicability of this new strategy for the validation of a chromatographic bioanalytical method and the good estimate of the measurement uncertainty without referring to any extra effort and additional experiments. A comparative study with the SFSTP approach [1] showed that both strategies have selected the same calibration functions.The holistic character of the measurement uncertainty compared to the total error was influenced by our choice of profile uncertainty. Nevertheless, we think that the adoption of the uncertainty in the validation stage controls the risk of using the analytical method in routine phase.     

Usefulness of capability indices in the framework of analytical methods validation

Analytical methods capability evaluation can be a useful methodology to assess the fitness of purpose of these methods for their future routine application. However, care on how to compute the capability indices have to be made. Indeed, the commonly used formulas to compute capability indices such as Cpk, will highly overestimate the true capability of the methods. Especially during methods validation or transfer, there are only few experiments performed and, using in these situations the commonly applied capability indices to declare a method as valid or as transferable to a receiving laboratory will conduct to inadequate decisions.     

Method validation procedures for environmental radiochemical measurements at AECS

The present paper describes the experience of the Atomic Energy Commission of Syria in relation to the application of Eurachem Guide on method validation for environmental radiochemical measurements. Methods validated include gamma and alpha spectrometry for natural and artificial radionuclides determination, and fluorometry determination for total uranium. Documents and records were first set to meet trackability and traceability requirements, where internal quality control mechanisms have been adopted. Methods stability was checked by means of Z-score control charts. Internal method validation parameters including method detection limits, repeatability limits, reproducibility limits, recovery coefficient and relative error were estimated. External method validation has been achieved by participating in international intercomparison exercises and proficiency tests organized by EML, IAEA and WU; some results of these activities are presented. Moreover, the application of both internal and external method validation gave the analysts in our laboratories more confidence in their skills, and it was of great assistance for our customers including regulatory authorities to evaluate the fitness of the method for their applications according to internationally agreed procedure. The steps followed here can be used for method validation in other laboratories with similar applications.     

Method validation and reference materials

For implementation of food and feed legislation, there is a strong need for development and harmonisation of reliable, validated and if possible, robust and simple analytical methods. In addition, precise methods used for measuring the exposure of humans to certain types of food contaminants and residues (natural, man-made or produced during technological treatment) such as, e.g. mycotoxins, acrylamide, pesticides and allergens have to be available, in order to compare results derived from monitoring studies. Methods should be validated (in-house or in a collaborative trial) according to harmonised protocols and good laboratory practice must be in place in order to be compliant with internationally harmonised standards. The way in which this is implemented depends strongly on the analyte, interference within the food matrix and other requirements that need to be met. Food and feed certified reference materials, when matrix matched and containing the appropriate concentration of the certified substance, are an extremely useful tool in validation of measurements.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany.     

Selectivity versus specificity in chromatographic analytical methods

  Analytical chemists should be aware of the differences between selectivity and specificity. Few analytical methods, including the chromatographic analytical methods, are truly specific. The International Union of Pure and Applied Chemistry (IUPAC) recommends that specificity is the ultimate of selectivity, therefore, analysts should promote this concept and aim to achieve highly selective analytical methods. Received: 30 September 1999 / Accepted: 17 January 2000     

Consideration of the uncertainty in the CRM value with the analysis of solid materials using atomic spectrometry

 The principles of the ISO "Guide to the expression of uncertainty in measurement" are applied to the analysis of solid materials by graphite furnace atomic absorption spectrometry. Assessment of trueness is achieved by the analysis of a certified reference material (CRM) under fixed instrumental conditions. For the evaluation of the method's uncertainty (as part of the validation) a model equation is derived, considering all significant contributions, including the uncertainty in the CRM value and the uncertainty in the CRM analysis. A concrete example is presented and discussed (soya flour as an unknown sample and CRM BCR rye grass). For routine analysis a pooled estimate from the validation experiment can be used, leading to an acceptable small uncertainty range even in the case of "duplicate determination". The test for trueness (acceptance) of the result of the CRM analysis is applied and the correction for detected bias is discussed. Received: 28 June 1998 · Accepted: 13 July 1998     

Method validation for the analysis of pesticide residues in grain by thin-layer chromatography

Method validation is an important requirement in the practice of pesticide residue analysis and is the process of verifying that a method is fit for its purpose. To make a correct decision on the validity of the method, the following method performance parameters have to be taken into consideration: scope, specificity, limit of detection, limit of quantification, linear range, accuracy, precision, repeatability, reproducibility, recovery, ruggedness and robustness. The goal of this study was to validate previously adapted thin-layer chromatographic methods for the pesticide residue analysis in grain. Confirmation of validation parameters for some compounds was also performed by gas chromatographic analysis.     

The traceability of analytical measurements

 Traceability to the System International (SI) is an important prerequisite for international comparability and uniformity of chemical measurements to ensure mutual recognition of the results. In theory, all measurements can be traced back to the seven base units of the SI. Although the traceability system works well for most physical measurements, in many analytical and in some spectrophotometric measurements this system is not satisfactory. This paper describes the particular and practical problems and the contribution of the Romanian National Institute of Metrology in this field. The paper discusses the following concepts: clearly defined targets in the form of requirement specification, knowledge of trueness and/or measurement uncertainty, and traceability through an unbroken chain of calibration to primary standards. Traceability and uncertainty being two concepts inherently coupled, two examples of assessment of the uncertainty of measurement results are given for two spectrophotometric methods currently used in chemical laboratories. Received: 17 July 1996 Accepted: 2 September 1996