Concentration exchangeable sites

To elucidate the higher BE peaks [S(2p) 168.9, 169.6 eV], we examined the Naflon film Itself because It has -SOj" cation exchange sites. Only C(ls) and F(ls) peaks were observed. No S(2p]f peak was observed even after Ar" bombardment. This result suggests that the surface concentration of cation exchange sites Involving -SO3 Is low. Sulfur located well below the surface would, of course, hot be detected by XPS, We assign the higher BE S(2p) peak to a surface sulfate species (11),... 

To allow for its numerical solution, we formalize our discussion of the ion exchange model by including in the basis a species Ap (e.g., >X Na+) representing the exchanging site (Eqn. 9.21). This species has a molal concentration mp, and the... 

Why might one be specifically interested in the chemistry of a particular species in soil From a positive perspective, it is desirable to provide plants with nutrients in forms that are available and yet are not present in concentrations high enough to cause environmental harm. Potassium ions are found in the soil solution and on exchange sites. Both species are available to plants. It may also be part of the mineral structure of soil, as in muscovite,... 

Several other nmr procedures have been used for the determination of fractionation factors. These have advantages in some systems. Instead of determining the effect of the concentration of an exchanging site on the averaged chemical shift, the effect on the averaged relaxation rate of water protons can be used in a very similar way (Silverman, 1981 Kassebaum and Silverman, 1989), For example, addition of the enzyme Co(ii)-carbonic anhydrase to an aqueous solution increases the observed value of XjT because the proton-relaxation rate is the average of that for the bulk solvent (cfl. 0.3 s ) and that for water bound to the cobalt ca. 6x 10 s ). The average is different in an H2O/D2O mixture if the bulk solvent and the Cobound solvent have different deuterium contents, and it has been used to determine a value for the fractionation factor of Co-bound water molecules in the enzyme. 

Ion exchange involves the formation and breakage of bonds between ions in solution and exchange sites in a zeolitic adsorbent. The reaction equilibrium of the ion exchange process depends most significantly on contact time, operating temperature and ionic concentration. 

When the test component content in the samples varies over a wider interval, a calibration curve must be constructed. Calibration curves with ISEs are usually linear over several concentration orders (usually from about 10" m to about 10" m) and their slope is close to the theoretical Nernstian value. Both at high and at low concentrations with respect to the linear part, the caUbration dependence becomes curved and, eventually, independent of the test substance concentration (see fig. 5.1). The upper limit of the ISE response is mostly given by saturation of the active sites in the electrode membrane (for example ion-exchange sites), whereas the lower limit is determined by solubility of the... 

Cation exchange and selectivity are processes involving the cationic concentration in solntion, the cation dimensions, and the confignration of the exchange sites. For cationic molecules, the retention properties follow the relation... 

In Figure 15-8, analyte ions equilibrate with ion-exchange sites at the outer surface of the ion-selective membrane. Diffusion of analyte ions out of the membrane creates a slight charge imbalance (an electric potential difference) across the interface between the membrane and the analyte solution. Changes in analyte ion concentration in the solution change the potential difference across the outer boundary of the ion-selective membrane. By using a calibration curve, we can relate the potential difference to analyte concentration. 

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