Newsletter No 2 June 2011

Reference materials


Ike van der Veen

cb june2The laboratory of IVM is heavily involved in both the preparation and testing of certified reference materials (CRMs), which are used to ensure the quality of analyses performed in European laboratories. CRMs contain a certified level of varying compounds like polychlorinated biphenyl (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), polyfluorinated compounds (PFCs) or other contaminants.

CRMs are available for diverse matrices, such as fish tissue, mussels, sediments, and water. They can be bought by laboratories to check their performance on analyses of target compounds in a certain matrix. Laboratories analyze the CRM in the same way as they perform analyses on real samples. The results are compared with the certified levels of the compounds in the reference material, which provides information on the performance of the laboratory on the specific analysis.

The Institute of Reference Materials en Measurements (IRMM) of the European Commission, located in the Joint Research Centre in Geel, Belgium, is responsible for the preparation and testing of CRMs. After preparation of a material, homogeneity tests are performed to ensure all lots (bottles, tins, ampoules) of the material contain exactly the same. In addition, a stability test is performed to make sure the material will be stabile for at least ten years.  IRMM invites laboratories to perform characterization studies. After a thorough comparison of the data and scrutinizing the technical conditions under which the laboratories carried out their analyses, IRMM assigns certified values to the reference material together with uncertainties.  Periodically IRMM invites laboratories to perform a characterization study to ensure the material is still stable.

Now IVM has become accredited, it is invited by IRMM on a regular basis to perform characterization studies, homogenization studies and stability tests on different compounds for a variety of reference materials.

Non-certified reference materials are used for interlaboratory comparison studies (ILS) or proficiency tests (PT schemes).  The main goal of such exercises is to improve the quality of analysis of individual laboratory by comparison with other laboratories. Because such a test is completely blind, it is the strongest quality tool in analytical chemistry, even stronger than the use of CRMs because a CRM comes with a certificate with the target values and their uncertainties, so the analyst knows what the answer should be. In those types of studies participating laboratories analyze the test material with their own in-house methods. A mean of all results, dependent of the statistics used without outliers, is calculated as well as the deviation of each laboratory from the mean. The calculated mean value is not necessarily the true value, as also a group of laboratories can make (systematic) errors, but it will be used as the assigned value.  Individual laboratory will be able to compare their own results with the assigned value and the relative standard deviation of the mean, which provides them with information about the performance of their analyses.

cb juneQUASIMEME (Quality Assurance of Information on Marine Environmental Monitoring in Europe), which finds its origin in an EU project in 1992, organizes proficiency tests on a large number of contaminants on a regular basis. IVM performs the homogeneity tests and analyses the materials for indicative levels to determine whether the materials are suitable or not for PT schemes for the specific compounds. IVM has also facilities to prepare test materials such as water samples and fish test materials. This is sometimes done within European research projects such as PERFOOD.

Often an ILS is coupled to one or more workshops, during which all the challenges and differences of methods of participating laboratories are compared and discussed.  In collaboration with QUASMEME, IVM organizes such workshops in conjunction with leaning exercises for new contaminant groups.

Recently, IVM has started a new stepwise-designed learning exercise on chlorinated paraffins for QUASIMEME.   Chlorinated paraffins are a highly complex mixture of chlorinated alkanes with different chain lengths. They are mainly being used as cutting oil in the metal industry. The compounds are persistent and bioaccumulate in fish. In particular in China, the production increases exponentially. Within the United Nations (UNEP) chlorinated paraffins are considered to be placed on the official persistent organic pollutants (POPs) list. The EU requires the analysis of these compounds for the Water Framework Directive. Laboratories are therefore eager to improve and validate their methods. The new study is envisaged to last ca. 3-4 years.

Contact: Ike van der Veen