Certified reference materials biological

NAA is a quantitative method. Quantification can be performed by comparison to standards or by computation from basic principles (parametric analysis). A certified reference material specifically for trace impurities in silicon is not currently available. Since neutron and y rays are penetrating radiations (free from absorption problems, such as those found in X-ray fluorescence), matrix matching between the sample and the comparator standard is not critical. Biological trace impurities standards (e.g., the National Institute of Standards and Technology Standard Rference Material, SRM 1572 Citrus Leaves) can be used as reference materials. For the parametric analysis many instrumental fiictors, such as the neutron flux density and the efficiency of the detector, must be well known. The activation equation can be used to determine concentrations ... 

In Wolf WR, ed. Biological Reference Materials, pp. 109-140. John Wiley Sons New York. Okamoto K and Fuwa K (1985) Certified reference material program at the National Institute for Environmental Studies. Anal Sd 1 206-207. 

Seawater studies require certified reference materials for biologically important dissolved components such as carbon (both inorganic and organic), nutrients, and trace metals, as well as for salinity, which is hydro-graphically important. A number of the committee s key recommendations therefore explicitly address these parameters. There is also a striking need for reference materials based on particulate matrices, where many of the analytical techniques used are matrix dependent and differ markedly... 

Denise LeBlanc is the Group Leader for the Marine Sciences Group and the Manager of the Certified Reference Materials Program at the Institute for Marine Biosciences (IMB) of the National Research Council of Canada. The Certified Reference Materials Program manufactures instrument calibration standards and certified reference materials for shellfish toxins, PCBs, PACs, and trace elements in marine sediments, in biological tissues, and in seawater. Her experience resides in the manufacture and long-term production of reference materials. 

The certification procedure for seven trace metals (Ba, Ca, Li, Mg, Mn, Na and Sr) in the certified reference material FEBS-1 (National Research Council Canada, Institute for National Measurement Standards, Ottawa, Canada) based on fish otolith matrix by isotope dilution - ICP-MS in comparison to ICP optical emission spectrometry and X-ray fluorescence analysis, is described by Sturgeon et al4X The isotope dilution technique is also employed for species analysis in biological systems,46 e.g., for the determination of mercury species in tuna material,54 or in aquatic systems using cold vapour ICP-MS.55... 

These biological factors also affect the reference materials. It is easy to envisage that different reference materials, all certified with respect to their mass fractions, could be derived from different cultivars or derived from different tissues (processed fractions) and would differ in their genetic make-up. This would result in different relative amounts of DNA for an identical mass fraction. Due to these biological factors these uncertainties can only be avoided if all producers of certified reference materials establish a system of comparable reference materials, accounting for the underlying biological factors. 

In this scheme, the primary reference material is defined as a chemical substance of the highest (and known) purity, or a well-characterized substance in a matrix, This classification of materials is, however, fairly arbitrary. It is ideal when used in connection with standards characterized in terms of biological activity. Primary standards are thus the International Reference Preparations (IRP) produced by the World Health Organization (WHO). In this case the primary standard for a particular antibiotic is the WHO reference preparation which constitutes the unit of that antibiotic. When people wish to use it they have to prepare a large batch of samples calibrated to the primary. This is then called a secondary standard. However, for well-defined chemical parameters, the term certified reference material is preferred. 

Definitions 2 and 3 allow an evolution in the different techniques and methods as definitive methods for the same analyte (Leijnse, 1982). Indeed, even though systematic errors were investigated during the initial research work, later technical advances may uncover errors that were undetected during the original measurements. The end use and end purposes of the definitive method include the evaluation of the accuracy of reference methods and its application to the quantitation of analytes in certified reference materials present in a biological matrix. 

The production of biological and environmental Certified Reference Materials (CRMs) is one of the main activities of the Institute for Reference Materials and Measurements (IRMM), Joint Research Centre of the European Commission, Geel (Belgium) (1). The Reference Materials Unit was therefore requested by the Istituto Superiore di Sanita (ISS), Rome (Italy) to perform the transformation of a batch of ca. 80 kg wet Antarctic coastal marine sediment, eollected in the Terra Nova Bay during the XI Italian Expedition to the Antarctic, into a sampled, dry and conservable powder to be certified for the content of a range of elements. 

Numerous standard or certified reference materials exist for verifying the reliability of new or modified methods, especially for total mercury standard reference materials for individual organomercury species can be more difficult to obtain. The existing methods for determining mercury in biological and environmental matrices are described more fully in the following sections. 

Padberg S, Burow M, Stoeppler M. 1993. Methyl mercury determination in environmental and biological reference and other materials by quality control with certified reference materials (crms). Fresenius J Anal Chem 346 686-688. 

Element speciation in biological materials is a difficult analytical task. The challenge is to identify and/or quantify very low concentrations of few to several target species (concentration values far below the total element content) in a complex chemical matrix. Additional difficulties include similar physicochemical properties exhibited by the species of one element and their chemical lability. Very often, not all element forms in the sample are known and, finally, the list of certified reference materials (CRMs) for speciation analysis is still limited. " The two most important features of an analytical tool suitable for speciation analysis are excellent selectivity and high sensitivity. Special care should be paid to preserve the natural composition and distribution of species in the sample during the entire procedure. 

This chapter presents the results of studies carried out for the determination of Pb, Cd, Hg and As using GC-MS. Since GC-MS requires a volatile form of the metal, suitable chelating agents were identified, prepared, and examined for the cross-over (memory) effect. Also the validation of isotope dilution GC-MS for the determination of these toxic metals in biological samples was carried out using suitable NIST certified reference materials. 

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