Needs for Specific Reference Materials

The need for a number of specific analyte and matrix RMs can be identified. Ihnat (1995) gives a very extensive overview of these needs. Quevauviller (1999) has reported on more recent work, undertaken in Europe to study future demand for RMs. Both authors identify a number of common themes, which may be summarized as follows. 

Total Elements There is a dearth of elemental concentration data for a wide range of nutritionally, toxicologically, clinically, and environmentally pertinent elements. Some of the elements for which total concentration information is still required, usually at the low end of concentration range but occasionally at the high end, are Al, Ba, B, Be, Br, Cs, F, I, Li, Mo, N, Pt, S, Sb, Si, Sn, Th, Ti, TI, U, V, W, rare earth elements, and radionuclides. Thus, it would seem advisable to certify each new RM for as many elements as possible so that certified values would be available for a larger number of elements in addition to the small number of core elements typical of many current RMs. 

Speciated Components Little information is available for RMs with respect to the chemical forms or species in which elements occur. In the first approximation, bioavaila-ble, extractable, or leachable levels of elements are of interest. Secondly, at a higher degree of sophistication, data on the levels of the actual species or inorganic moieties such as nitrate, ammonium, phosphate, bromide, bromate, iodide, iodate, and molecular species of which the elements are constituents would be of relevance to those conducting mechanistic and speciation research. Reference materials that are certified for extractable elemental concentrations are not available to monitor the usual procedures in soil science based on extraction. 

As usually viewed by the reference material producers, a fundamental philosophy of certification rests on the concept of independent methodology, which is the application of theoretically and experimentally different measurement techniques and procedures to generate concordant results leading to one reliable assigned value for the property. Such assigned values are thus method-independent. Extractable concentrations are generated by specific procedures and are thus method-dependent, an idea that has to be rationalized with the fundamental method-independent concept in reference material certification work. 

---