Inter-laboratory method trials

The NADA method approval process consists of three phases (1) method development by the sponsor and generation of information to establish that the method satisfies acceptability criteria (2) FDA review of the sponsor s data to determine suitability of the method and (3) the method trial , an inter-laboratory study, which determine whether the method meets performance criteria when used in multiple laboratories. The inter-laboratory method trial procedure provides an indication of a method s ability to be used as a practicable and reliable regulatory tool. Sponsors are urged to develop methods that are mgged and exceed rather than meet the minimal standards of acceptability. Those methods that appear marginally acceptable after review often do not pass the inter-laboratory method trial. 

Within the EU, there was an almost complete abandonment of inter-laboratory method trials to characterize performance of methods used in veterinary dmg residue... 

Within CEN TC 275, a distinct protocol for the conduct of inter-laboratory method validation trials is not selected or required, but it is recommended to apply ISO 5725 or the ISO/International Union for Pure and Applied Chemistry (lUPAC) harmonized protocol. " In the past, results of several national and international interlaboratory trials had been accepted. Nevertheless, the following fundamental aspects of the harmonized protocol for the design of method-performance studies should be fulfilled ... 

Important part of validation procedure is prognosis (on basis of Phai macopoeial requirements and results of inter-laboratory trials) of sample preparation, final analytical operation and total uncertainties. It enables to forecast method uncertainty in control laboratories. 

Further applications have to be expected because in several inter-laboratory trials the CE has performed to be as good as and often better than chiral HPLC. The recently reported separation of timolol enantiomers using a /7 p 3 /s(2,3-di-0-methyl-6-0-sulfo)-j5-cydodex-trin under non-aqueous buffer conditions is indicative of the good performance of the method. 

After many years of debate and discussion, there is now an international consensus about the statistical approach and method to be employed in full collaborative trials This topic is discussed further in Section 9.5. The lUPAC protocol referred to above requires the analysis of duplicate test samples of the same material (a minimum of five materials or, exceptionally, three) in eight or more laboratories. However, there are many occasions where inter-laboratory studies are needed which, for various reasons, cannot achieve the prescribed criteria. In instances where the lUPAC criteria cannot be achieved, it is recommended that the Youden Matched Pairs procedure is used. The statistics of the method have been recently updated and a new procedure described. 

A common example where ANOVA can be applied is in interlaboratory trials or method comparison. For example, one may wish to compare the results from four laboratories, or perhaps to evaluate three different methods performed in the same laboratory. With inter-laboratory data, there is clearly variation between the laboratories (between sample/treatment means) and within the laboratory samples (treatment means). ANOVA is used in practice to separate the between-laboratories variation (the treatment variation) from the random within-sample variation. Using ANOVA in this way is known as one-way (or one factor) ANOVA. 

Once a method is established, precision may be determined by suitable replicated experiments. However it is in inter-laboratory trails that the problems with environmental methods often show up. It is accepted that for trace analysis RSD values of tens of percent are likely. In studies conducted in Western Australia on pesticide residues in bovine fat RSD values for dieldrin were 12% and for dia-zonium were 28%. It is typical to see a quarter of the laboratories in such a trial producing values that could be termed outliers. In the previously mentioned study, 5 laboratories out of 26 had z> 3 for aldrin. In a parallel study RSD values for petroleum in dichloromethane and water were 40% and 25%, respectively. The conclusions of these studies was that there was poor comparability because of the different methods used, that accreditation apparently made no difference to the quality of results, and that a lack of understanding of definitions of the quantities to be analysed (for example gasoline range organics ) caused non-method errors. In relation to methods, this is contrary to the conclusion of van Nevel et al. who asserted that the results of the IMEP round of analyses of trace elements in natural and synthetic waters showed no dependence on method [11]. If properly validated methods do yield comparable results, then one conclusion from the range of studies around the world is that many environmental methods are not validated. It may be that validated methods are indeed used, but not for exactly the systems for which they were validated. 

The aim of this trial was to validate MARA by evaluating the performance of the assay at different laboratories worldwide. The method of implementation of the testing could have been considered in the same perspective as a collaborative trial used to validate a standard method. The trial was viewed with potential to form the basis of laboratory proficiency testing defined by ISO as determination of laboratory testing performance by means of inter-laboratory comparisons (Horowitz, 1988). 

ISO 5725 (BSI 5497, 1987), Precision of test methods, Part 1 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory trial, 1986. 

In a protocol about collaborative studies [10] it is also considered what is called preliminary estimates of precision. Among these the protocol defines the total within-laboratory standard deviation . This includes both the within-run or intra-assay variation (= repeatability) and the between-run or inter-assay variation. The latter means that one has measured on different days and preferably has used different calibration curves. It can be considered as a within-laboratory reproducibility. These estimates can be determined prior to an interlaboratory method performance study. The total within-laboratory standard deviation may be estimated fi-om ruggedness trials [10]. 

The essential question in the inter-comparison of analytical methods is, If the same sample (or a set of identical aliquots of a sample) is analysed by the same method in different laboratories, are the results obtained the same within the limits of experimental error . It is apparent, therefore, that the selection of an appropriate sample or samples is critical to this question and that the sampling stage should be carried out by a skilled sampler with an understanding of the overall context of the analysis and trial. 

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