Speciation extraction

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

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. 

Speciation involves a number of discrete analytical steps comprising the extraction (isolation) of the analytes from a solid sample, preconcentration (to gain sensitivity), and eventually derivatisation (e.g. for ionic compounds), separation and detection. Various problems can occur in any of these steps. The entire analytical procedure should be carefully controlled in such a way that decay of unstable species does not occur. For speciation analysis, there is the risk that the chemical species can convert so that a false distribution is determined. In general, the accuracy of the determinations and the trace-ability of the overall analytical process are insufficiently ensured [539]. 

With the exception of GC-MIP-AES there are no commercial instruments available for speciation analysis of organometallic species. Recently, a prototype automated speciation analyser (ASA) for practical applications was described [544,545], which consists of a P T system (or focused microwave-assisted extraction), multicapillary GC (MC-GC), MIP and plasma emission detection (PED). MCGC-MIP-PED provides short analysis times ([Pg.676]

Figure 3.3. Changes of Cd speciation in soil solutions of Cd nitrate-treated Domino soil from California (data extracted from Candelaria and Chang, 1997)...

Figure 3.4. Effects of phosphate levels on Cd and Zn solution speciation in California soils that received sludge application (data extracted from Villarroel et al., 1993)...

Figure 3.5. Effects of Cl concentrations (NaCl or CaCl2) on Cd solution speciation in a California soil (data extracted from Bingham et al., 1983)...

Ho M.D., Evans G.J. Operational speciation of cadmium, copper, lead and zinc in the NIST standard reference materials 2710 and 2711 (Montana soil) by the BCR sequential extraction procedure and flame atomic absorption spectrometry. Anal Commun 1997 34 353-364. 

Kheboian C., Bauer C. Accuracy of selective extraction procedures for metal speciation in model aquatic sediments. Anal. Chem 1987 59 1417-1423. 

Kim, N.D. and Fergusson, J.E., Effectiveness of a commonly used sequential extraction techniques in determining the speciation of cadmium in soils. Sci Total Environ 1991 105 191-209. 

Tessier, A., Campell, P.G.C., and Bisson, M., Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 1979 51 844... 

Koch, K. R. Miller, J. Westra, A. N. On the liquid-liquid extraction of Pt(IV/II) from hydrochloric acid by N-Acyl(aroyl)-N, N -dialkylthioureas a multinuclear (1H, 13C and 195Pt) NMR speciation study of the extracted complexes. International Solvent Extraction Conference, Cape Town, South Africa, Mar. 17—21, 2002, 327-334. 

A recent method [ 114] for the speciation of organotin compounds in seawater combines solid-phase extraction, online HG, and GC with MIAE. This method enjoys a 0.5 pg detection limit for tin. 

Accurate speciation of tributylstannyl ions in the presence of other degradation products was carried out by a.c. polarography, directly on the organic extract, without derivatization101. The degradation of tributyltins in aqueous solution was studied by differential pulse polarography102. 

Between pH values of ca. 6 and 12 aqueous solutions hold very little dissolved beryllium because of the low solubility of Be(OH)2. When the pH is raised above 12, the hydroxide begins to dissolve with the formation of, first, Be(OH)3 and then, at even higher pH values, Be(OH) (52). The presence of these species in strongly alkaline solutions was confirmed by means of solvent extraction experiments (90) and infrared spectroscopy (31). A speciation diagram is shown in Fig. 7, which was constructed using the values of log /33 = 18.8 and log /34 = 18.6 critically selected from Table III. The diagram illustrates clearly the precipitation and dissolution of Be(OH)2. 

The development of sensitive and rapid analytical schemes for the extraction and separation of inorganic tin and organic tin compounds and their chemical speciation products from water, sediments, and biological materials (WHO 1980 Reuhl and Cranmer 1984 Hall and Pinkney 1985 Laughlin and Linden 1985 Thompson et al. 1985 Blunden and Chapman 1986 USPHS 1992). 

Soil geochemistry is widely applied in mineral exploration, and with advancing knowledge of speciation and residence phases of trace elements in soils, a variety of partial and selective extractions for chemical analysis have been developed over the past decades. Each of these methods has been designed to target and dissolve only those elements that are adsorbed onto labile phases in soil, from carrier fluids and gases that transported them from a deposit to the surface (e.g. Hall etal. 1996). 

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