Natural Matrix SRMs

CRMs for Contaminants in Environmental Matrices For nearly two decades NIST has been involved in the development of SRMs for the determination of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and chlorinated pesticides in natural environmental matrices such as fossil fuels (Hertz et al.1980 Kline et al. 1985), air and diesel particulate material (May and Wise 1984 Wise et al. 2000), coal tar (Wise et al. 1988a), sediment (Schantz et al. 1990, 1995a Wise et al. 1995), mussel tissue (Wise et al. 1991 Schantz et al. 1997a), fish oil, and whale blubber (Schantz et al. 1995b). Several papers have reviewed and summarized the development of these environmental matrix SRMs (Wise et al. 1988b Wise 1993 Wise and Schantz 1997 Wise et al. 2000). Seventeen natural matrix SRMs for the determination of organic contaminants are currently available from NIST with certified and reference concentrations primarily for PAHs, PCBs, chlorinated pesticides, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofiirans (PCDFs) see Table 3.11. 

Tab. j.n NIST natural matrix SRMs for the determination of organic contaminants in environmental samples... 

N 1ST Analytical Approach for the Certification of Organic Constituents in Natural Matrix SRMs... 

If the sample and standard have essentially the same matrices (e.g., air particulates or river sediments), one can go through the total measurement process with both the sample and the standard in order to (a) check the accuracy of the measurement process used (compare the concentration values obtained for the standard with the certified values) and (b) obtain some confidence about the accuracy of the concentration measurements on the unknown sample since both have gone through the same chemical measurement process (except sample collection). It is not recommended, however, that pure standards be used to standardize the total chemical measurement process for natural matrix type samples chemical concentrations in the natural matrices could be seriously misread, especially since the pure PAH probably would be totally extracted in a given solvent, whereas the PAH in the matrix material probably would not be. All the parameters and matrix effects. Including extraction efficiencies, are carefully checked in the certification process leading to SRM s. 

Vitamins and Other Nutrients in Food Matrices see also Section 6.3. Food matrices are available with values assigned for vitamins, carotenoids, fatty acids, cholesterol, natural toxins, veterinary drugs, and hormone residues. The NIST food matrix SRMs for vitamins include coconut oil (SRM 1563), infant formula (SRM 1846), and baby food composite (SRM 2383) (particularly for carotenoids). Fatty acids and cholesterol are the primary analytes of interest in meat homogenate (SRM 1546) and diet... 

Stability Assessment In general there is no formal stability study prior to the certification of a natural matrix S RM. H owever, the stability of the certified analytes is monitored on a regular basis, typically every 1-3 years depending on the analytes, as the SRMs are analyzed as control samples during the analyses of similar matrix samples. A recent study of PAHs in frozen mussel tissue over nearly 10 years found no significant changes in the concentrations of the measured PAHs (Schantz et al. 2000). 

Zeisler R (2000a) Investigations by INAA for the Development of Natural Matrix Standard Reference Materials (SRMs) Suitable for Small Sample Analysis. J Radioanal Nucl Chem 245 73-80. 

Several organizations (e.g., NIST, NRC-Canada, and IAEA) provide sediment reference materials containing radionuclides, many of which are only certified for artificial radionuclides ( Cs, Sr, Am, and Pu). Certain specific radionuclides have no certified natural matrix materials, including ocean, lake, and river sediments. Although these sediments are certified for a few naturally occurring and artificial radionuclides, the extent of radioactive equilibrium of the uranium and thorium decay series in these environmental materials is not provided. NIST currently offers an ocean sediment Standard Reference Material (SRM 4357) in... 

Accelerator mass spectrometry (AMS) is useful to measure extremely low-abundance nuclides (isotope ratio of 10 to 10 relative to its stable isotope), such as Be, C, A1, C1, " Ca, and I, in natural samples. Small amounts of C and T can be measured by AMS on mg size samples of carbon and iodine extracted from 500-ml seawater samples (Povinec et al. 2000). Neutron activation analysis (NAA), radiochemical neutron activation analysis (RNAA), and inductively coupled plasma mass spectrometry (ICP-MS) are useful for the determination of ultra-trace Th and U in geological and cosmochemical samples, and for determination of the concentration of Pu and Pu. Reference marine-biological samples are necessary to test the performance of the analytical methods employed in surveying and monitoring radioactive materials in the sea. An ocean shellfish composite material containing 0.1% w/w Irish Sea mussel, 12% w/w White Sea mussel, and 87.9% w/w Japan Sea oyster has been prepared as the NIST SRM 4358 (The National Institute of Standards and Technology, SRM) in the natural-matrix, environmental-level radioactive SRM series (Altzitzoglou 2000). This NIST SRM 4358 sample will be useful for the determination of the activity of K, Cs, Pb, Ra, Th, and Am. 

Both GC and LC methods are widely utilized in the determination of PAHs. Wise, Sander, and May [16] describe the advantages and limitations of LC-based methods for PAHs, and compare the results of LC fluorescence (LC—FL) with GC—MS measurements used in the certification of natural matrix standard reference materials (SRMs). GC with mass spectrometric detection offers the potential for high-resolution and selective separations of complex matrix samples. GC separations of PAHs are limited, however, by coelution of certain isomers with methyl-polysiloxane stationary phases (e.g., chrysene and triphenylene [228 u] benzo[li]fluoranthene, benzo[y]fluoranthene, and benzo[fc]fluoranthene [252 u] and dibenz[fl,c]anthracene and dibenz[fl,/z]anihracene [278 u]). GC separations of isomers have been achieved by use of liquid crystalline stationary phases and other phases in combination with optimized methods. 

Tab. 3.6 Examples for BCR, NIST and NRCC natural biological and environmental matrix CRMs/ SRMs certified for elements...

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