Sample analysis proficiency-testing

There are two main types of proficiency testing scheme. First, there are those set up to assess the competence of a group of laboratories to undertake a very specific analysis, e.g. lead in blood or the number of asbestos fibres in air collected on membrane filters. Secondly, there are those schemes used to evaluate the performance of laboratories across a certain sector for a particular type of analysis. Because of the wide range of possible analyte/matrix combinations it is not practicable to assess the performance of laboratories when analysing all the possible sample types. Instead, a representative cross-section of analyses is chosen (e.g. determination of different pesticide residues in a range of foodstuffs or the determination of trace levels of metals in water samples). 

There is no experimentally established optimum frequency for the distribution of samples. The minimum frequency is about four rounds per year. Tests that are less frequent than this are probably ineffective in reinforcing the need for maintaining quality standards or for following up marginally poor performance. A frequency of one round per month for any particular type of analysis is the maximum that is likely to be effective. Postal circulation of samples and results would usually impose a minimum of two weeks for a round to be completed and it is possible that over-frequent rounds have the effect of discouraging some laboratories from conducting their own routine quality control. The cost of proficiency testing schemes in terms of analysts time, cost of materials and interruptions to other work has also to be considered. 

We also can take suitable data from a proficiency test (PT). In this case the laboratory must have participated in the PT successfully. We also have to consider, if the PT covered all relevant uncertainty components and steps of analysis. This includes e.g. if the matrix of the PT sample was similar to routine samples. If this is the case, we again calculate U from 2 Sr. 

CX/MAS 02/12 (2002), Codex Alimentarius Commission, Codex Committee on Methods of Analysis and Sampling (FAO/WHO), Validation of methods through the use of results from proficiency testing schemes, agenda item 8c of the 24th session, Budapest, Hungary, Nov. 18-22, 2002. 

Quality control sample, often chosen randomly, from a batch of samples and undergoing separate, but identical sample preparation and analysis whose purpose is to monitor method precision and sample homogeneity. Duplicate testing also aids in the evaluation of analyst proficiency. Volume 1(10). 

On the basis of this framework from the CWC, the Technical Secretariat and the OPCW Laboratory have built a complex network of linked procedures for sampling and analysis and related activities. Experience gathered during inspections, training, exercises, and proficiency tests led to improvement... 

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 ... 

Matrices most used were soil, water, and organic liquids. Other matrices used were, for example, a polymer strip in the first proficiency test, a metal strip covered with a thin layer of paint in the third proficiency test, and a wipe sample in the fourth proficiency test. In the ninth and tenth proficiency tests, an emulsion sample and decontamination solutions were introduced. Not all sample matrices employed in the past are considered realistic. During the Preparatory Commission of the OPCW, the Task Force on Analytical Issues (see Fourth Report of the Expert Group on Inspection Procedures, PC-VIII/B/WP.12, dated September 20, 1994) discussed that sample matrices such as wipe, rubber, paint, and concrete will be extracted on site and sent as extracts off site for analysis, after splitting. 

Only chemicals that are considered relevant within the scenario of the proficiency test are to be reported to avoid irrelevant chemicals being reported, in real off-site sample analysis, confidential information on the facility under inspection is revealed (e.g. information on an industrial production process that is not relevant to the implementation of the CWC). This requirement is a consequence of Paragraph C.17 of the Confidentiality Annex of the CWC, l1. The reporting of irrelevant chemicals is penalized with immediate failure of the test see Section 6.1. 

After arrival, checking, and coding, the proficiency test samples and corresponding matrix blanks are usually divided into portions to allow application of multiple sample preparation methods for the different analytical techniques prior to analysis (9). 

Method 3, however, poses an additional challenge to the participants if no reference standard is available because it implies that the participants must have the chemical synthesized. Laboratories that are capable of synthesizing CWC-related compounds, in general, show a high competence in the analysis of authentic/proficiency test samples. Commercially available Scheduled compounds, alcohols, and thioalcohols are listed in Annex 2. 

The analysis strategy described shows what a tremendous amount of work the analysis of proficiency test samples actually holds. This example is just one approach that could possibly lead to successful completion of the analysis within the short timeline of the test. In practice, there may, of course, be other approaches leading to a similar result. 

Proficiency Test versus Off-site Sample Analysis... 

Lewisite 1 was used for spiking in the sixth and in the ninth proficiency test. The participants that failed to identify lewisite 1 did not describe an effective lewisite 1 sample preparation procedure (12) in their analysis report, which could indicate that no such procedure had been employed. The participants performances in the identification of lewisite 1 are summarized in Table 3. 

Methylphosphonic acid was used for spiking in the fifth and in the tenth proficiency test. Many participants, in particular, failed to identify methylphosphonic acid in the tenth test for reasons that are difficult to trace from their analysis reports. It can only be speculated that the high concentration of salt ( %% NaCl) in the sample has been the cause most of these participants did not describe an effective sample preparation procedure (e.g. cation exchange) for the removal of salts, and employed GC/MS as an indirect analysis technique. Indirect GC/MS analysis of methylphosphonic acid requires derivatiza-tion salts are known to influence the derivatization reaction negatively. The participants performances in the identification of methylphosphonic acid are summarized in Table 6. 

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. 

There were differences identified in the degree of difficulty between the first 10 proficiency tests. These differences are a result of the changing sample composition, that is, different matrices, spiking chemicals, and background materials. It is mainly a laboratory s experience in the analysis of CWC-related chemicals that seems to allow the participants to cope with these varying challenges. The Technical Secretariat tries to maintain a similar degree... 

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. 

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. 

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