Physical speciation

Gdaniec-Pietryka, M., L. Wolska, and J. Namiesnik. 2007. Physical speciation of polychlorinated biphenyls in the aquatic environment. Trends Anal. Chem. 26 1005-1012. 

Physical speciation takes place when different forms of the same chemical species have to be determined in a sample. Examples include adsorbed forms, dissolved forms, complex forms, and so on. 

Lanson B, Drits VA, Gaillot AC, Silvester E, Plangon A, Manceau A (2002) Structure of heavy metal sorbed bimessite. Part 1. Results from X-ray diffraction. Am Mineral in press Latrille C, Elsass F, van Oort F, Denaix L (2001) Physical speciation of trace metals in Fe-Mn concretions from a rendzic lithosol developed on Sinemurian limestones (France). Geoderma 100 127-146 Lindsay WL (1979) Chemical equilibria in soils. John Wiley Sons, New York... 

Fernandez Alvarez F, Temero Rodriguez M, Fernandez Espinosa AJ et al (2004) Physical speciation of arsenic, mercury, lead, cadmium and nickel in inhalable atmospheric particles. Anal Chim Acta 524 33-40... 

Nearly all of the important chemical (identification of elements, purity, homogeneity, speciation) and physical (roughness, thickness, serie of the layers) parameters of such a structure can be determned non-destructively by X-ray methods (e.g., EDXRS, WDXRS, TXRS, SYXRS, g-XRS, NEXAFS). 

Several factors can influence metal uptake by stream autotrophic biofllms in fluvial systems. These include chemical factors (pH, saUnity, phosphate concentration) which affect metal bioavailabiHty by either altering the speciation of the metal or by complexing it at the biotilm s matrix and cell surfaces [18, 40], and also other biological and physical factors. 

New developments are, however, needed to make a major step forward in the field of speciation analysis. The first part, isolation and separation of species, may be the easiest one to tackle. For the second part, the measurement of the trace element, a major improvement in sensitivity is needed. As the concentration of the different species lies far below that of the total concentration (species often occur at a mere ng/1 level and below), it looks like existing methods will never be able to cope with the new demands. A new physical principle will have to be explored, away from absorption spectrometry, emission spectrometry, mass spectrometry, and/or more powerful excitation sources than flame, arc or plasma will have to be developed. The goal is to develop routine analytical set-ups with sensitivities that are three to six orders of magnitude lower than achieved hitherto. 

Chemical and physical properties of the contaminant should also be investigated. Solubility in water (or other washing fluids) is one of the most important physical characteristics. Hydrophobic contaminants can be difficult to separate from the soil particles and into the aqueous washing fluid. Reactivity with wash fluids may, in some cases, be another important characteristic to consider. Other contaminant characteristics such as volatility and density may be important for the design of remedy screening studies and related residuals treatment systems. Speciation is important in metal-contaminated sites. 

An evaluation of the fate of trace metals in surface and sub-surface waters requires more detailed consideration of complexation, adsorption, coagulation, oxidation-reduction, and biological interactions. These processes can affect metals, solubility, toxicity, availability, physical transport, and corrosion potential. As a result of a need to describe the complex interactions involved in these situations, various models have been developed to address a number of specific situations. These are called equilibrium or speciation models because the user is provided (model output) with the distribution of various species. 

Hemphill CP, Ruby MV, Beck BD, Davis A, Bergstrom PD. 1991. The bioavailability of lead in mining wastes physical/chemical considerations. Chem Speciation and Bioavailability 3(3/4) 135-148. 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

Sample Effects The recovery of an analyte from a complex matrix may be affected by other components of the matrix. The homogeneity of the sample will also influence the results. This is related to the issue of sampling mentioned above. Physical or chemical form can lead to incomplete recovery of the analyte. For example, an element may exist in more than one oxidation state in a sample and hence be incompletely determined by a method that requires it to be in one particular state only (speciation). The sample and/or analyte may be unstable, causing a change in the composition of the sample during the course of the analysis. 

Cadmium is a silver-white, blue-tinged, lustrous metal that melts at 321°C and boils at 767°C. This divalent element has an atomic weight of 112.4, an atomic number of 48, and a density of 8.642 g/cm3. It is insoluble in water, although its chloride and sulfate salts are freely soluble (Windholz et al. 1976 USPHS 1993). The availability of cadmium to living organisms from their immediate physical and chemical environs depends on numerous factors, including adsorption and desorption rates of cadmium from terrigenous materials, pH, Eh, chemical speciation, and many... 

XAS provides a powerful probe of both physical and electronic structure of an element within a sample, and has the ability to determine the molecular level speciation of As, Mo and Se over the concentration range of 50 pg/g to several weight percent (typical of mine tailings solids) (Brown et al. 1998) at the micron to mm scale. 

Buffle, J. and Horvai, S. eds. (2000). In Situ Monitoring of Aquatic Systems. Chemical Analysis and Speciation. Vol. 6, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems, Series eds. Buffle, J. and van Leeuwen, H. P., John Wiley Sons, Ltd, Chichester. 

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