Types of CRMs

In practice, CRMs are of the same use as RMs. The main advantage of using a CRM lies in the availability of the certified value, which is a key to achieve trueness. As the CRMs are certified with fully validated methods, following strict quality control procedures and within selected laboratories, the uncertainty of the certified value is also a key element for the user. 

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Certified reference materials (CRMs) to validate measurements of organic constituents were introduced in the early 1980 s, more than a decade after the development of the first natural matrix CRMs for inorganic constituents. There are three types of CRMs to support measurements of organic constituents ... 

Error 2 The use of CRMs is mentioned, but the type of CRMs not mentioned, nor the results of their analysis. Hellou et al. (1999) determined PCBs, DDTs, chlorda-nes, dibenzo-p-dioxins (ds), dibenzofurans (Fs), PAHs and sulphur heterocycles in marine harbor sediments. 

BERM-y recognized the need for interdisciplinary approaches for preparation of certain types of CRMs, partly in response to the measurement needs arising from governmental regulations dealing with food safety and environmental health criteria. 

Depending on the type of property value to be certified and the type of CRM, there may be differences in the approach applied. Matrix CRMs cannot be certified on the basis of direct mass determinations of constituents. Calculable (primary) and relative (rarely comparative) methods have to be used often after a total transformation or removal of the matrix. For such matrix CRMs there are three possible approaches certification within one laboratory using one so-called definitive method by two or more independent analysts ... 

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