Expert laboratories

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... 

Values stated on reference materials are conventional trae values. The results are usually obtained by independent methods in different expert laboratories. The conventional tme value should be close enough to the trae value. 

A result obtained by using several independent methods in several expert laboratories on one measurand Is regarded as conventional true value of a quantity... 

Another possibility is to choose expert laboratories, which are able to measnre with high precision reference methods, ntilising traceable calibration materials. If these laboratories use methods based on different physieo-chemical principles and eome to more or less the same result, it is very probable that the value is elose to the true value. 

There might be doubts among the participants if the result of the expert laboratories deviates from the mean of the participants... 

Analysis by an expert laboratory of high metrological quality. This will often be one or more reference laboratories such as a national measurement institute. 

Validation attempts in tlie field of drug residue analysis have demonstrated that die requirement for a full collaborative trial at the ideal level, while desirable, is sometimes impractical. Limiting factors for completing ideal multilaboratory validation studies are usually the high cost, lack of sufficient expert laboratories willing to participate in such studies, and overall time constraints. Hence, a three-laboratory validation study is often applied (16). 

Assessment in an expert laboratory(ies) using standard reference materials or samples of known composition. 

The analysis of the natural carotenoid pigments found in orange juice, for example, is extremely complex and should be left to an expert laboratory. However, the quantitative analysis of added /3-carotene and/or /3-apo-8 -carotenal to an orange drink or dilutable is much easier as pure standards are commercially available and these compounds can be readily separated using HPLC. 

The second major, and growing, route is the use of HPLC and either UV or fluorescence detection. Here vitamins are extracted from the product and then assayed using HPLC. This is another very specialised area and is often best left to an expert laboratory, as there may be problems with interferences and losses due to such factors as oxidation during extraction. 

Most FTMS instrument and method development research has been focussed on demonstration experiments. Examples include coupling FTMS with various sample introduction schemes (e.g., GC, LC, supercritical fluid chromatography), sample ionization (e.g., LD, pulsed SIMS, Cf-252 PDMS, etc.), and demonstrating application to various interesting classes of chemical compounds. These demonstrations are useful because they are indications of the potential of the technique. However, few reports of the routine use of FTMS for trace analysis, for accurate mass, and for structure determination of unknowns have yet appeared. One reason is that FT mass spectrometers are not widely spread in the hands of users. Another is that FTMS is not yet routine. Most of the demonstration experiments have been done in expert laboratories by committed and highly focussed graduate students and postdoctoral researchers. 

Direct comparison with certified reference materials Homogeneity testing results A primary method of chemical measurement Consensus value from expert laboratories Consensus of participants... 

Traceability is not really a new fundamental concept in the field of laboratory medicine. Many years before the concept traceability had been mentioned in general chemical metrology, reference measurement procedures and reference materials had been established in clinical chemistry. Some basic experimental work for the development of reference measurement procedures and reference materials had already been undertaken in expert laboratories. 

Fig. 3 The diagrams show some of the results of an inter-laboratory trial undertaken with UK expert laboratories based on determination of Cd in an artificial food digest matrix containing a known amount of Cd. The values obtained by the laboratories using (i) their conventional calibration are compared with those from (ii) an approximate matching IDMS procedure developed and validated at LGC...

As a consequence of EU Directive 78/142/EEC, which introduced a limitation of vinyl chloride monomer both as residual amount in final articles (QM lmg/kg) intended to come into contact with foodstuffs and in migration to food (SML not detectable LOD 0.01 mg/kg), the corresponding necessary analytical methods were developed between several European expert laboratories and laid down as agreed methods in EU Directives 80/766/EEC and 81/432/EEC, respectively. This piece of the EU harmonization process was too time- and work-consuming to continue in this way. The vinyl chloride Directives therefore remain a unique feature in EU food packaging legislation since this was found to be impractical for generalization. 

As for IMEP, the CRV is derived from measurement results reported by reference laboratories in a certibcation campaign. These reference laboratories are usually NMIs and expert laboratories that have well-established, demonstrated... 

The CIPM-MRA is a transparent process to underpin measurement capability claims of signatories to the meter convention. Key comparisons are organized for NMIs or designated laboratories to demonstrate the equivalence of their measurements in view of mutual acceptance of national standards and reference measurements. Their reported results and the equivalence statements of the measurements are included in the Appendix B of the CIPM-MRA, which can support the CMCs in Appendix C of the CIPM-MRA. Once reported there is no possibility of withdrawal of measurement results. Conversely, in a CCQM pilot study results could be withdrawn, but participation does not result in equivalence statements in Appendix B of the CIPM MRA. Therefore, participation in CCQM pilot studies was recently extended to invited expert laboratories. The results of both CCQM key comparisons and pilot studies are published in the Technical Supplement of Metrologia [24], The IRMM assists the CIPM to support the MRA by making... 

Thanks are extended to Catherine Harrison and Brian Owens for their expert laboratory assistance and to Norman Ford of Precision Detectors, Inc. for assistance and enlightening discussions on the light-scattering instrument used in this study. 

The proficiency testing materials should be prepared by characterization in expert laboratories and the target value and the associated combined uncertainty should be assigned according to ISO Guides 30-35. ... 

The new European Chocolate Directive [14] allows the addition of up to 5% of vegetable fats other than cocoa butter (CB), the so-called cocoa butter equivalents (CBEs), in chocolate. CBEs resemble the chemical composition and physical properties of CB very closely, making them therefore extremely difficult to quantify and even in some cases to detect (especially at very low levels). There is a perceived need within official control laboratories for reliable analytical methods for the quantification (around the 5% level) of CBEs in chocolate, as Member States laws and administrative provisions need to comply with the new Chocolate Directive before August 2003. All proposed analytical methods have been evaluated by the JRC in collaboration with EU expert laboratories [15]. The performance of several methods has been compared and a final method based on the analysis of the main components, triglycerides, has been proposed for further validation. 

Interlaboratory studies carried out by consortia of European laboratories, of which the aim is improve the state-of-the-art of different types of measurements [7], These projects are useful to detect possible sources of errors related to particular techniques, to create networks of laboratories within the European Union and to prepare groups of expert laboratories for the certification of reference materials... 

---