Interlaboratory tests, quality control

Interlaboratory survey, collaborative interlaboratory survey, quality control survey, multicenter evaluation a system for evaluating the accuracy and precision of reference methods conducted by individual clinical chemical laboratories, and for assessing the performance of analytical instruments Samples of the same specimen are analysed by different laboratories, and the range of interlaboratory scatter is determined for the particular analytical technique. In some countries, it is now mandatory for clinical chemical laboratories to participate is such quality assurance surveys, and those failing to fulfil requirements for a particular analyte may not be recognized by medical insurance companies. Similar surveys are conducted to test the reliability, accuracy, precision, running costs and ease of operation of new instru-... 

It must be remarked that terminology is not consistent and there are many widely used synon)ms. Quality control in this Chapter refers to practices best described as internal quality control. Quahty assessment is often referred to as external quality control, proficiency testing, interlaboratory comparisons, round robins or other terms. Internal Quality Control and External Quality Assessment are preferred because they best describe the objectives for which the RMs are being used, i.e. the immediate and active control of the results being reported from an analytical run or event, and an objective, retrospective assessment of the quality of those results. 

The previous chapters of this book have discussed the many activities which laboratories undertake to help ensure the quality of the analytical results that are produced. There are many aspects of quality assurance and quality control that analysts carry out on a day-to-day basis to help them produce reliable results. Control charts are used to monitor method performance and identify when problems have arisen, and Certified Reference Materials are used to evaluate any bias in the results produced. These activities are sometimes referred to as internal quality control (IQC). In addition to all of these activities, it is extremely useful for laboratories to obtain an independent check of their performance and to be able to compare their performance with that of other laboratories carrying out similar types of analyses. This is achieved by taking part in interlaboratory studies. There are two main types of interlaboratory studies, namely proficiency testing (PT) schemes and collaborative studies (also known as collaborative trials). 

Youden, W.J. (1959), Graphical Diagnosis of Interlaboratory Test Results, Industrial Quality Control, 15(11), 24,... 

Interlaboratory tests are a powerful tool for external quality control (see chapter 15). A laboratory should take part wherever possible. The participation has to be planned. The results and if necessary the corrective actions have to be documented. Procedures have to be accordingly described in the quality manual. 

Procedures carried out in the laboratory, as opposed to proficiency testing or other interlaboratory collaborations, are known as in-house or internal quality control procedures. When running batches of samples with calibration solutions and unknowns, there are a number of extra samples that can be analyzed that cover different aspects of quality control (QC samples). These QC samples should be documented in the quality manual and be part... 

Maier, E A., Quevauviller, Ph, and Griepink, (1993), Interlaboratory studies as a tool for many purposes proficiency testing, learning exercises, quality control and certification of matrix materials. Analytica Chimica Acta, 283 (1), 590-99. 

What would the resulting Youden plots look like if the method was rugged If the method was not rugged If the laboratories were precise, but each was biased If the laboratories were imprecise, but accurate [See, for example, Youden, W.J. (1959). Graphical Diagnosis of Interlaboratory Test Results , Industrial Quality Control, 24(May), p. 24.]... 

The ISO/IEC GUIDE 25 [1] stresses, in paragraphs 5.6 and 9.3, the importance of participation in proficiency testing programs or other interlaboratory comparisons, as appropriate and when suitable programs are available. This would imply that such activities are an important part of a laboratory s quality control procedures. 

The terms inter-laboratory quality control, laboratory proficiency testing, or external surveillance surveys are commonly given to tiie evaluation of the interlaboratory v iation tiiat is expected when the stime delay that dsts between tiie actual laboratory analysis of the sexternal quality assessment is more propriate. 

Control samples should have a high degree of similarity to the actual samples analyzed otherwise, one cannot draw reliable conclusions on the measurement system s performance. Control samples must be so homogeneous and stable that individual increments measured at various times will have less variability than the measurement process itself. Quality Control samples are prepared by adding known amounts of analytes to blank specimens. They can be purchased as certified reference material (CRM) or may be prepared in-house. In the latter case, sufficient quantities should be prepared to allow the same samples to be used over a longer period of time. Their stability over time should be proven and their accuracy verified, preferably through interlaboratory tests or by other analysis methods. 

The IAEA helps the ALMERA network of laboratories to maintain their readiness by coordination activities, by development of standardized methods for sample collection and analysis, and by conducting interlaboratory comparison exercises and proficiency tests as a tool for external quality control. 

Nowadays it is generally accepted that laboratory proficiency testing schemes are an important quality assurance tool in environmental monitoring programmes. Apart from using validated analytical methods and internal laboratory quality control procedures, the regular participation of laboratories in interlaboratory comparisons is required to ensure the accuracy and comparability of data. 

Such an approach was trialled in the late 1990s as part of an initiative by the Environment Agency in the UK. It led to proposals for a quality control scheme for use within the Agency s Direct Toxicity Assessment programme for effluent assessment and control. The trial entailed an interlaboratory ring-test of four test methods using two toxicants (3,4-dichloroaniline and zinc sulphate) from which accuracy and precision criteria were estimated, as described below. 

Quality Assurance/Quality Control Validation of steps and analytical results throughout, by independent or reference method(s), application of CRMs, RMs, contiol materials (internal QC), interlaboratory comparisons, proficiency tests to validate accuracy and precision competent analyst/specialist... 

Since important decisions affecting the health and welfare of humanity must be made on the basis of analytical results, considerable effort must be directed toward assuring greater confidence in the reliability of the output of analytical laboratories. The Commission of the European Communities, after performing a study to determine the comparability of chemical analyses for drinking water quality, concluded that analytical quality control must be required as a routine component of analytical work. They state ( ), "Only the combination of intralaboratory controls of precision and accuracy complemented by interlaboratory intercomparison tests can lead to a significant evaluation and improvement of analytical results."... 

The quality control (QC) tests discussed in Sections 10.5 and 11.2.9 are integral parts of QA designed to check results. Some QC measures are prompt indicators that warn of problem occurrence at the time of analysis others are delayed indicators that require backtracking to And when a problem first arose. Control charts for radiation detector operation are an example of a prompt indicator of reliability. Records of deviations from the norm in an analysis or a measurement may also be prompt indicators if immediately considered. Periodic blank, blind, and replicate analyses, especially interlaboratory comparisons, are delayed indicators for which results may not be available for days or weeks after a problem has arisen. Review and assessment of compiled data are delayed indicators of information quality. 

There are other routinely practiced procedures in terms of intralaboratory and interlaboratory quality control, such as the control chart, round-robin interlaboratory testing, and various proficiency tests offered by different agencies, such as the PATs (Proficiency Analytical Testing) by AHA in the US and WASPs (Workplace Analysis Scheme for Proficiency) by the Health and Safety Laboratory in Great Britain. In normal circumstances, a combination of these quality control measures should be used in performing workplace air analysis. 

One of the corner stones of quality control procedures is the analysis of test material by a number of laboratories, the so-called interlaboratory studies. The... 

Continued emphasis may be expected on interlaboratory testing and establishment of precision and bias for standard test methods. Equally necessary for quahty control is extensive evaluation of the product forms of interest to establish acceptance criteria that discriminate between satisfactory and unsatisfactory material. While rapid and inexpensive tests will be used for most quality control tests, an increase in more sophisticated techniques such as electrochemical testing and slow strain rate techniques is expected. Additional work is necessary to improve reproducibility of rusting, pitting/crevice, and SCC tests. In some cases, control of the specimen potential may improve test reproducibility. 

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