Reference materials proficiency testing

Among the elements of quality control in mycotoxin analysis, proficiency tests, control materials (reference materials and certified reference materials), traceability in spiking, and recovery checks have been demonstrated to be particularly relevant. 

Where possible, there should be participation in external quality assessment ( proficiency testing ) using material with reference measurement values. 

The direct and immediate use of laboratory data in medical diagnostic decision making is unique, so the proper use of reference materials in conjunction proficiency testing clinical chemistry is vital if false and mis diagnosis is to be avoided. 

A number of international organizations are active in the field of clinical chemistry reference materials and proficiency testing, these include ... 

As the use of RMs increases and international trade in these materials becomes established, it has become clear that they can be subject to high levels of import duty and delay when clearing customs. In 1998 ISO/REMCO established Task Group 6 to investigate the problems involved in shipping reference materials (and materials that are in the process of being made into reference materials, such as proficiency testing materials) across national boimdaries. 

Millar RC, Armishaw P, Wilson MC, Majewski l.M (1995), Recent developments in Australia-reference materials and proficiency testing. Fresenius J Anal Chem 352 28-32. 

Over the past decade, a major trend has been the development of the use of proficiency testing (PT) or evaluation materials (Fox 2000). PT materials are a type of reference material, which aid in assessment of analytical laboratory measurement quality. There will be an increased use of such materials as part of laboratory accreditation programs and other new quality assurance efforts, including internal audits. At the same time, a number of providers have used PT schemes to produce a form of RM intended to meet the ever-growing need for RMs required for routine QC use (Jenks 1995,1997). 

Magnitude of the response caused by a certain amount of analyte Alternatively, certified reference materials, samples analyzed with reference methods or proficiency test materials may be apphed... 

The previous chapters of this book have discussed the many activities which laboratories undertake to help ensure the quality of the analytical results that are produced. There are many aspects of quality assurance and quality control that analysts carry out on a day-to-day basis to help them produce reliable results. Control charts are used to monitor method performance and identify when problems have arisen, and Certified Reference Materials are used to evaluate any bias in the results produced. These activities are sometimes referred to as internal quality control (IQC). In addition to all of these activities, it is extremely useful for laboratories to obtain an independent check of their performance and to be able to compare their performance with that of other laboratories carrying out similar types of analyses. This is achieved by taking part in interlaboratory studies. There are two main types of interlaboratory studies, namely proficiency testing (PT) schemes and collaborative studies (also known as collaborative trials). 

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. 

Contaminated Land Proficiency Testing Scheme Control of Substances Hazardous to Health Certified Reference Material cumulative sum... 

There are different reasons for interlaboratory tests. One is method validation, e.g. prior to the standardization of characterization of reference materials, which have to be certified. The third and most important for quahty assurance is proficiency testing of laboratories. There are different requirements for each type of interlaboratory test. 

The samples that are used for proficiency tests should be similar to routine samples in order to get an information about the routine capabilities of the laboratory. In some cases it is useful to distribute a larger amount of sample than is needed for the determination, to give the laboratories the opportunity to use this material as an in-house reference material. But the surplus can be also used to cany out more analyses compared to routine, which is not desired. 

Traditionally, the education that chemists and chemistry laboratory technicians receive in colleges and universities does not prepare them adequately for some important aspects of the real world of work in their chosen field. Today s industrial laboratory analyst is deeply involved with such job issues as quality control, quality assurance, ISO 9000, standard operating procedures, calibration, standard reference materials, statistical control, control charts, proficiency testing, validation, system suitability, chain of custody, good laboratory practices, protocol, and audits. Yet, most of these terms are foreign to the college graduate and the new employee. 

Proficiency testing is an activity in which the competence of the workers in a laboratory, or set of laboratories, is determined. This is done by comparing the results obtained for a sample or reference material with either the results of the other laboratories (real sample) or with the true answer (reference... 

Analytical method validation forms the first level of QA in the laboratory. Analytical quality assurance (AQA) is the complete set of measures a laboratory must undertake to ensure that it is able to achieve high-quality data continuously. Besides the use of validation and/or standardized methods, these measures are effective IQC procedures (use of reference materials, control charts, etc.), with participation in proficiency testing schemes and accreditation to an international standard, normally ISO/IEC 17025 [4]. Method validation and the different aspects of QA form the subject of Section 8.2.3. 

Residue-testing laboratories might also need to review their sample preparation processes and consider modifying or eliminating tissue homogenization prior to residue extraction. Suppliers of proficiency-testing services should also question whether certain drugs are appropriate to include in such studies. For example, liver spiked with sulfaquinoxaline, sulfadiazine, or sulfamerazine is not suitable for preparation of spiked interlaboratory check samples or reference materials. 

Analyzing control materials alongside the test samples greatly improves proficiency in mycotoxin analysis. Certified reference materials (CRMs) represent ideal control materials, due to their statement of uncertainty and traceability, and they should be routinely used as much as possible. Unfortunately, as outstanding as the improvements made in the last decade have been, even though the list of CRMs in the area of mycotoxins is rather long, it is still insufficient. A list of the available reference materials in the mycotoxins area is reported in Table 1 the issue has been reviewed by Boenke (27). 

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. 

However the chemical community has not been dormant in the period since the Convention of the Meter came into being. A vast range of analytical methods has been developed with ever increasing sensitivity and selectivity. Comparability of measurement results has been achieved in many sectors by the use of collabora-tively studied methods, reference materials, check samples and proficiency testing schemes. It is only recently that steps have been taken to develop traceability to international standards. In developing this traceability much can be learnt from the way traceability has developed for physical measurements. 

More and more decisions based on chemical measurement are having global effects. Reference materials are important tools to obtain global comparability of results of chemical measurement. However, the use of validated analytical methods and the proof of personal skills by proficiency testing are other tools of the same rank (Fig. 1) [1],... 

To conduct a proficiency test, a reference laboratory will prepare a quantity of material appropriate for distribution to all the laboratories under test. Requirements for the material will include that it is well characterized, and that it is sufficiently stable and homogeneous that no tested laboratory will be put at disadvantage by receiving a sample not representative of the lot. Further, the material should be typical of that of interest, and have constituents with concentrations within the ranges of interest. Additionally, it is important that concentration values be kept confidential during the period of the test, so that no participant will have an unfair advantage. 

The proficiency test provider and reference laboratory may be the same organizational entity. If not, they must closely coordinate and document their quality assurance procedures and division of responsibilities. For a test round to be successful, each laboratory under test must receive a sample which is the same as every other sample from the lot, within the limits specified for the test. This means that careful attention must be given to material packaging, stability, and handling during distribution. 

Extension into physical metrology is less obvious, but has no conceptual barrier. The direct approach could be applied if proficiency tests were conducted by a reference laboratory distributing to device producers, preparing lots of material measures and calibrants such as gage blocks, masses, or thermometers. Distribution of such material measures is already a feature of most measurement assurance programs in physical metrology. Use of the indirect approach would have units randomly selected from production and sent to a reference laboratory. This could prove, in some cases, more economical than direct proficiency testing of the producers of the devices. 

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