Interlaboratory test

The principle of insignificancy , enabling use of the given principle for any level of probability is substantiated. The systematic application of the given principle results in developing metrological criteria for pharmaceutical reference substance, analytical validation, evaluation of results of interlaboratory testing and suitability of the analytical equipment for the phamiaceutical analysis. 

Environmental analytical association Ecoanalytica produce standai d samples during last 12 years. Two topics will be discussed. The first is the principles of development of staictures and maintenance of quality of standai d samples. The organization of manufacture and maintenance of their stability ai e considered too in the report. Besides them authors consider scientifically-methodical aspects of preparation of samples for experimental check of technical competence of analytical laboratories and also samples for interlaboratory tests. 

Davies, P. L., Statistical Evaluation of Interlaboratory Tests, Fresenius Z. Anal. Chem. 331, 1988, 513-519. 

Analytical laboratories need to check their performance with regard to the production of accurate results with satisfactory precision. The most desirable way to ensure the reliability of analytical results is the participation of laboratories into regular interlaboratory tests. An interlaboratory study has to be understood as a study in which several laboratories measure a quantity in one or more identical portions of homogeneous, stable materials under documented conditions, the result of which are compiled into a single document (IUPAC [1994] Prichard et al. [2001]). 

Proficiency testing is a special type of laboratory performance studies defined as study of laboratory performance by means of ongoing interlaboratory test comparisons (ISO Guide 33 [1989] ISO/REMCO N 280 [1993] IUPAC [1993] Prichard et al. [2001]). Proficiency testing is an essential part of external quality assessment schemes and performance checks. 

Study of laboratory performance by means of ongoing interlaboratory test comparisons". 

Details of the interlaboratory test on the precision of the method are to be summarised in an annex to the method. It is to be stated that the values derived from the interlaboratory test may not be applicable to analyte concentration ranges and matrices other than given in annex. 

Year of interlaboratory test and reference to the test report (if available)... 

Certification through interlaboratory testing. In this case, the reference/certified value is obtained by pooling results from several laboratories that have demonstrated capability in analyzing the analyte(s) of interest. The various laboratory means are manipulated statistically to determine the best or truest estimate of the value of interest. 

Interlaboratory Test Series of measurements of one or more quantities performed independently by a number of laboratories on samples of a given material. 

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

Youden, W. J. "Interlaboratory Tests-Chapter Three" NBS Special Publication 300. Vol. 1, 1969. 

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. 

Participation in interlaboratory test should be a matter of course for each laboratory in its testing field... 

The other method uses data from interlaboratory tests directly. 

We have seen two different approaches to estimate the measurement uncertainty. One was using data from control charts, CRM analysis, PT results and/or recoveiy tests and sometimes maybe also experience of the analyst, the other was just using the reproducibility standard deviations from interlaboratory tests. In most cases the second method delivers higher estimates. 

If retained sample material from an interlaboratory test is available and it is stable after the test is finished, this also can be used as an in-house reference material. 

There are different reasons for interlaboratory tests. One is method validation, e.g. prior to the standardization of characterization of reference materials, which have to be certified. The third and most important for quahty assurance is proficiency testing of laboratories. There are different requirements for each type of interlaboratory test. 

The third type of interlaboratory tests is proficiency testing (PT) for laboratories. The objective here is to get an indication of the performance of the laboratoiy. The laboratory should work under routine conditions to get a realistic indication of its performance. A PT can not only be a help for the laboratoiy to improve its capabilities, but also can be used by customers or regulatory bodies for the selection of qualified laboratories. 

First of all it takes time to evaluate a PT. So it is quite a long time before the laboratory knows the result. The interlaboratory test is retrospective. It is therefore not possible to base quality management only on proficiency tests. 

Since interlaboratory tests are a great logistical challenge, especially if there are a lot of participants, the personnel of the provider must have special organizational capabilities. To understand the problems associated with the analyses there must be technical... 

The selection and preparation of the samples very often is the most crucial item in an interlaboratory test. All characteristics that could affect the integrity of the test have to be considered. This includes homogeneity and stability, which are dealt with in detail later. The PT provider has to look for possible changes in and the effect of ambient conditions on the samples. 

On the basis of an interlaboratory test of die method using viscous, heavily-pigmented materials which tended to form a surface film, the within-laboratory standard deviation was found to be 3F(1-7C) and the between-laboratory standard deviation was found to be 7 F(3-9C). Based on these standard deviations, the following criteria should be used for judging the acceptability of results at a 95% confidence level ... 

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