Ion speciation

Town, R. M. and Filella, M. (2000). Dispelling the myths is the existence of LI and L2 ligands necessary to explain metal ion speciation in natural waters Limnol. Oceanogr., 45, 1341-1357. 

In some cases, resins have been used to try to determine only the plant or more generally the biological availability of an ionic species. Resins placed in soil have also been used to study ion speciation, soil microbiology, various phosphorus measurements, soil nutrient supply rate, nutrient transformations and movement, and micronutrient and metal toxicity [22-25],... 

Since [Fe(lll)]jojaj [Fe " ], the formation of ion pairs and complexes is greatly enhancing the equilibrium solubility of ferrihydrite. This is called the salting-in effect and illustrates why mineral solubility calculations in seawater must take ion speciation into consideration. 

The effect of solids on ion speciation is not limited to precipitation/dissolution reactions. Most solid surfaces in seawater possess a net negative charge that enables them to electrostatically attract cations (M ). This attraction can be represented as ... 

Concentration values are more often required in analytical practice than activities (except for certain fields in clinical analysis and metal ion speciation in... 

Instrumental Methods in Metal Ion Speciation, Imran AH and Hassan Y. Aboul-Enein... 

The carbonato complexes of lanthanides and actinides are of importance with regard to the metal ion speciation in the environment. These are, however, not linked with the enzyme models for carbon dioxide hydration and hence are not dealt with in further detail. 

The concentrations of the major inorganic ions in seawater are well known in estuarine and coastal areas as well as in interstitial waters anomalies in their constant ratios may occur. The major cations are Na+, Mg2+, Ca2+, K+ and Sr2+, the major anions Cl-, SCty2-, HCO3", B(OH) ", F" and Br". Ion pairs involving these elements and H+, OH", CO32-, POif3- and SiOz -. Under anoxic conditions the S2- - ion and bi- and polysulphides become important. A summary of the major ion speciation in seawater is given by Kester et al. (1975). 

I. Ah, H.Y. Aboul-Enein, Instrumental methods in metal ions speciation Chromatography, capillary electrophoresis and electrochemistry, New York Taylor Francis (2006). 

Das, A.K. and Chakraborty, R. (1997) Electrothermal atomic absorption spectrometry in the study of metal ion speciation. Fresenius J. Anal. Chem., 357, 1-17. 

Langford, C.H. and Gutzman, DW (1992) Kinetic studies of metal ion speciation. Anal. Chim.Acta, 256, 183-201. 

Lu, Y., Chakrabarti, C.L., Back, M.H., Gregoire, D.C. and Schroeder, W.H. (1995) Kinetic studies of metal ion speciation using inductively-coupled plasma mass spectrometry. Int. 

The species distributions shown in Table 12.2 depict results from one of the earliest (Garrels and Thompson, 1962) and one of the most recent (Millero and Schreiber, 1982) seawater ion pairing models. These results and others (Kester, 1975a) are consistent with the following general characteristics of major ion speciation in seawater ... 

Since equilibrium constants are defined by ion activities, which are defined by their concentrations and coefficients (see equation 4.15), they do not include ion pairing or complexation effects. In a multi-ion and multiligand solution, where ion pairing is common, it is necessary to use thermodynamic equilibrium constants to convert the ion-pair concentrations to concentrations of free ions. This equilibrium constant (Kc) is defined by concentrations, making it useful to compute ion speciation. The thermodynamic equilibrium constant (K q) used in calculating Kc is based on the following conditions I = 0 m, 25°C and 1 atm. Thus, Kc is defined by the following equation ... 

The solubility of mineral salts may be enhanced with the formation of ion pairs, a salting-in effect, requiring the inclusion of ion speciation effects. Conversely, there is commonly a salting-out effect of dissolved constituents across a salinity gradient. This can be particularly important when examining more hydrophobic organic compounds (HOC), such as aromatic hydrocarbons in estuaries. 

Cances, B., Ponthieu, M., Castrec-Rouelle, M., Aubry, E., and Benedetti, M. F. (2003). Metal ions speciation in a soil and its solution Experimental data and model results. Geoderma 113(3—4),... 

II. ION SPECIATION ON CLAY MINERAL SURFACES A. Diffuse Ion Swarm... 

Another approach to the assessment of ion speciation in the resin and solution phases with equal ility for the determination of formation constants of complexes in these two environments is provided by NMR spectroscopy. The method can provide sharp, well-separated signals for each successive complex species formed, the peak area being proportional to the atomic concentration of the element being measured, irrespective of its complex form. For a completely labile system, a well-defined chemical shift change is often observed with successive complex formation. These features make this analytical procedure well suited for study of metal ion complexation by the ion-exchanger phase. 

In another example, five test cases were computed by PHREEQE and EQ3/6 and the same thermodynamic database was run for each program (INTERA, 1983) to test for any code differences. The five examples were speciation of seawater with major ions, speciation of seawater with complete analysis, dissolution of microchne in dilute HCl, reduction of hematite and calcite by titration with methane, and dedolomitization with gypsum dissolution and increasing temperature. The results were nearly identical for each test case. Test cases need to become standard practice when using geochemical codes so that the results will have better credibility. A comparison of code computations with experimental data on activity coefficients and mineral solubilities over a range of conditions also will improve credibility (Nordstrom, 1994). 

Huber C., Filella M., and Town R. M. (2002) Computer modelling of trace metal ion speciation practical implementation of a linear continuous function for complexation by natural organic matter. Comput. Geosci. 28, 587-596. 

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