Designated laboratories proficiency testing

ISO, IUPAC and AOAC INTERNATIONAL have co-operated to produce agreed protocols on the Design, Conduct and Interpretation of Collaborative Studies 14 and on the Proficiency Testing of [Chemical] Analytical Laboratories .11 The Working Group that produced these protocols has prepared a further protocol on the internal quality control of data produced in analytical laboratories. The document was finalised in 1994 and published in 1995 as the Harmonised Guidelines For Internal Quality Control In Analytical Chemistry Laboratories .12 The use of the procedures outlined in the Protocol should aid compliance with the accreditation requirements specified above. 

Collusion might take place between laboratories so that independent data are not submitted. Proficiency testing schemes should be designed to ensure that there is as little collusion and falsification as possible. For example, alternative samples could be distributed within a round. Also instructions should make it clear that collusion is contrary to professional scientific conduct and serves only to nullity the benefits of proficiency testing. 

If data are normally distributed, the mean and standard deviation are the best description possible of the data. Modern analytical chemistry is often automated to the extent that data are not individually scrutinized, and parameters of the data are simply calculated with a hope that the assumption of normality is valid. Unfortunately, the odd bad apple, or outlier, can spoil the calculations. Data, even without errors, may be more or less normal but with more extreme values than would be expected. These are known has heavy-tailed distributions, and the values at the extremes are called outliers. In interlaboratory studies designed to assess proficiency, the data often have outliers, which cannot be rejected out of hand. It would be a misrepresentation for a proficiency testing body to announce that all its laboratories give results within 2 standard deviations (except the ones that were excluded from the calculations). 

The method of analysis is either prescribed, when this is regulated by law, for example, or the choice is left to the participant. In the latter case the method is reported with the result. In keeping with the aims of a proficiency testing scheme, the method used should be the routine method employed by the laboratory, and not some enhanced protocol designed to improve performance in the scheme. 

Laboratory accreditation bodies also offer formal recognition (accreditation) of proficiency testing providers to ILAC-G13 2000 (International requirements for competence of providers of proficiency testing schemes). This process is intended to provide confidence that proficiency testing schemes are designed and conducted to internationally acceptable standards. 

OPCW) provides a proficiency-testing scheme for the analysis of samples in the context of the CWC. The design of the scheme should simulate off-site sample analysis, whereas the objective of the scheme is to obtain a network of laboratories that are qualified for the aforementioned task. Successful participation in the scheme may lead to this qualification, that is, designation, provided a laboratory has obtained an accreditation for the analysis of CWC-related chemicals by an internationally recognized accreditation body. 

The OPCW proficiency-testing scheme is set up with the objective to simulate off-site sample analysis in order to select (i.e. designate) laboratories that are capable of the following, with a high level of confidence ... 

Designated laboratories or laboratories seeking designation must participate in one of the usually two proficiency tests conducted annually. The proficiency tests conducted within the same year should therefore have the same degree of difficulty in order to accommodate a fair and consistent proficiency-testing scheme among the participants. 

Figure 11. The degree of difficulty of proficiency tests 1 to 10, measured for the designated laboratories...

The laboratories participating in the OPCW proficiency-testing scheme until December 2002 can be divided into a group of 13 designated laboratories and a group of 30 nondesignated laboratories ... 

Figure 17. Frequency and type of participation of the designated laboratories in proficiency tests 1 to 10...

Another element is the use of a cocktail of different Scheduled chemicals in a single proficiency test. Applying a cocktail of chemicals may not be very realistic, however, it is considered unavoidable in order to train participants in the analysis of as many different Scheduled chemicals as possible in a small number of tests. The chemicals, used for spiking the samples, have been reviewed, which revealed that certain Scheduled chemicals have not been covered in the first 10 proficiency tests. Therefore, it would be recommendable to include such chemicals in future scenarios. The same recommendation applies to several identified categories of chemicals, which have been applied in previous proficiency tests, but created difficulties (repeatedly) for some of the designated laboratories, as well as for most of the nondesignated laboratories that regularly participate in the scheme. 

As a result of the first ten official OPCW proficiency tests, the Technical Secretariat has designated 13 laboratories out of the approximately 22 regular participants worldwide. The performance of these 22 laboratories has been studied in detail, which revealed areas of strengths and weaknesses for each of them. The latter information may become useful for the Technical Secretariat when selecting designated laboratories for the analysis of authentic samples and when identifying particular training requirements. 

These designated laboratories performed unsuccessfully in the sixth official OPCW proficiency test This designated laboratory performed unsuccessfully in the tenth official OPCW proficiency test... 

The OPCW Laboratory conducts a Proficiency Testing program (as described in Chapter 6) for the purpose of selecting and maintaining designated laboratories. The OCAD has been used extensively by all laboratories participating in the tests and will undoubtedly be an important reference in any event of off-site analysis. 

Before the designation, the laboratories developed their laboratory methods for testing, constructed and made operational their laboratory quality system and obtained its accreditation, and continued the participation and successful performance in the OPCW proficiency tests (PT). Analytical methods in particular and a certain level of quality assurance systems have existed in the laboratories, involved often in research, well before their designation. Participation in the international interlaboratory... 

Sample preparation procedures and analytical techniques for the off-site laboratories of the CWC have been developed and tested in five international interlaboratory comparison (round-robin) tests (1 5), in two trial proficiency tests, and in more than 14 official proficiency tests (see Chapter 6). The Recommended Operating Procedures (ROPs) for sampling and sample preparation (6,7) were written and updated on the basis of the results of the round-robin tests. The ROPs (see Table 1) were designed to be comprehensive enough to allow the analysis of all CWC-related chemicals. Accordingly, some of the procedures contain many sample preparation steps. It is also recommended that the ROPs should be used as first choice in the analysis, with other approaches not excluded. 

Table 3. Sample types in trial and official proficiency tests arranged by the OPCW for selection and testing of designated laboratories...

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