Proficiency-testing samples

Provided the sample matrix and analyte concentration are appropriate, matrix Certified Reference Materials (CRMs) can make ideal proficiency testing samples. The assigned value is the certified value given on the certificate accompanying the CRM. The certificate will also give an uncertainty estimate for the certified value, and the use of CRMs allows the traceability of analytical data to be established. However, matrix CRM availability is limited and the materials are often expensive. Hence, Certified Reference Materials are seldom used as PT samples. 

In this case, the assigned value is obtained from data produced by a number of expert laboratories who have analysed the proficiency testing sample by using a recognized reference method. The laboratories must be able to demonstrate their... 

Little concrete information is available on the proportion of private biomonitoring laboratories that have attained CLIA certification, but CLIA regulations impose substantial penalties on noncomplying laboratories (CDC 2004). Because proficiency test samples and standard reference materials for analytes not typically measured may be unavailable (CMS 2005), comparability of private-laboratory results with reference ranges developed elsewhere may be open to question. 

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). 

Handling and preparation of authentic/proficiency test samples is preferably performed in a laboratory room dedicated to this purpose. The key advantage of a separate room is limitation of the possibilities of sample contamination. In previous tests, several participants have experienced cross-contamination, often with the consequence of false positive identifications and subsequent failure of the test. 

Parallel to the preparation of proficiency test samples, some laboratories do prepare quality control samples by the same methods, to check... 

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. 

EN17 Daggett, S.G., Greenberg, N. and Peters, C. (1991). Examples of non-physio-logical interferences in external quality control (proficiency test) samples that affect accuracy assessment. Clin. Chem. 37, 959, Abstr. 234. 

L/S ratio results show considerable differences among laboratories. For proficiency testing samples LM-09 and LM-10 from the CAP, the reported CVs were 26% (at mean L/S = 4,46) and 27% (at 2.31), respectively. ... 

College of American Pathologists proficiency test samples, Human Serum NIST SRMs Na Acidify, spike with Mg [N/MT] Determine Na with ICP-MSr from Na/ Mg ratio in a manner similar to that used in IDMS [ICP-MS] [N/MT-ICP- MS[ Long and Vetter (2002)... 

The proof of method applicability has been achieved by analysing proficiency test samples separately validated by reference methods. See the typical reconstructed compound specific mass chromatograms in Figure 4.145. 

To further assess performance, analysis of six proficiency test samples were analysed.Results of the analysis of the six soil samples were in agreement with the published reference values (Figure 5). 

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