While in principle, proficiency testing could be applied in most chemical measurement sector, it is by its nature more readily applicable in particular circumstances. One important consideration, particularly for scheme organizer, is the minimum number of participating laboratories needed to ensure the technical viability of a proposed PT schemes. This factor will be especially important in those schemes using the mean of participant’s results to determine the assigned values of test materials. When this is the case the general view of organizers of lab proficiency testing schemes us that the minimum number of participants should be at the least 10 and preferably 30 if a scheme is to be technically viable. However where the assigned value is established independently of participants results, it would be possible in principle, to run a PT sachem fir a single laboratory of curse an important feature affecting minimum size is fiance. As most PT schemes are paid for from the fees paid by participants, another important consideration for organizer is the minimum participant numbers required to ensure the fanatical viability of schemes.
From the viewpoint of participant a proficiency testing schemes is most applicable as a quality assurance procedure where the laboratory has a large throughput of routine samples and tests of the type covered by the PT scheme. In these circumstances the laboratory can incorporate the PT materials into their routine work schedule without the need to make special arrangements for their analysis. This course is how proficiency testing should always be tackled by analytical laboratories, so that the performance assessment obtained is a useful reflection of the quality if routine work. Where routine throughput is small, a laboratory may find that the costs of participation in a PT scheme are large in relation to the income they generate from their day to day work from the particular tests concerned.
Despite this however the survey of participants showed that there are instances where laboratories find proficiency testing applicable to their situation even though they have little routing work in the tests concerned. Such benefits as staff training, maintenance of expertise and demonstration of a commitment to quality were cited by these laboratories. Usually therefore proficiency testing is most readily applicable where a large number of laboratories are regularly carrying out at least moderate numbers of routine analyses. In such circumstances, the need for a regular assessment and demonstration of the quality of routine data is self evident. Meeting such a need through proficiency testing is likely to be technically and economically feasible.
Proficiency testing is especially relevant to test sectors where reference materials are difficult or impossible to obtain. The materials distributed in a PT schemes, while of a lower petrological level than certified reference materials are nevertheless well-characterized for the analyses of interest and therefore provide a vital substitute for CRM where the latter are enviable. In this context the establishment of schemes for environmental analysis for example, might be considered of higher priority in terms of promoting valid measurements, than the establishment of schemes for metallurgical analysis, where CRM are readily available.
Proficiency testing is especially appropriate where a wide variety of analytical methods are in use for a given demonstrate. However, where analytical methodology is non-routine or under development, proficiency testing is hardly applicable. In such cases there is no sound basis for establishing assigned values. Furthermore, a PT schemes could not be relied upon to give an accurate assessment of laboratory proficiency testing. Performance scores attributed to laboratories would be just as likely to reflect inherent problems in methodology rather than laboratory competence.
Finally it may be noted that the nature of the test materials themselves may impose a limitation on the type of PT scheme that can be organize. Very hazardous materials might pose insuperable safety problems in relation to predation and distribution of the materials. Likewise it may be impossible to organize proficiency tests for very labile analyses.
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