Sorption processes ionic strength

Solid phase extraction (SPE) involves the separation of components of samples in solution through their selective interaction with and retention by a solid, particulate sorbent. SPE depends on differences in the affinities of the various components of the sample for the sorbent. The mechanisms of the interactions are virtually identical to the sorption processes that form the basis of liquid chromatographic separations (p. 80). The choice of solvent, the pH and ionic strength of aqueous solutions, and the chemical nature of the sorbent surface, especially its polarity, are all of importance in controlling the selectivity and efficiency of an extraction. 

The partition coefficients for different LAS homologues (Table 5.4.2) are higher in the marine environment due to the higher ionic strength that promotes sorption of anionic surfactants [14] and an increase in the partition coefficient with the alkylic chain length has been observed (Table 5.4.2). The evolution of the concentration of the various homologues of LAS in solids in suspension (cf. Fig. 5.4.2) is similar to that found in water and, in the process of adsorption, an increase can be observed in line with the chain length, as commented on previously. 

Ionic strength and pH are closely related, and their influence on the sorption process may be explained by electrostatic or chemical interactions. The ionic strength of the medium is correlated positively... 

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

The variety of mechanisms that may be involved in the sorption process of metal ions onto activated carbon induces a great number of factors that control the adsorption the surface oxygen complex content, the pH of point of zero charge, the pore texture of carbon, the solution pH and its ionic strength, the adsorption temperature, the nature of the metal ion given by its speciation diagram, its solubility, and its size in adsorption conditions. The influence of these various conditions is detailed in Section 24.2.1.4. 

Many parameters as, e.g, pH, the ionic strength or the metal saturation affect the p/Ca s of the functional groups and thus the interactions between the metal ions and the humic material. Fortunately, however, detailed information on these interactions is not required, as long as film diffusion is the rate determining step of the sorption process. All we have to know in this connection is according to Eq. [8] or [11] the separation factor a (or the and the ion-exchange capacity C. These quantities depend of course on the above interactions, but they can be determined independently and without any detailed information on the sorption mechanism. 

The principal abiotic processes that transform strontium in soils and sediments are mediated by sorption and desorption reactions between the soil solution and matrix (precipitation, complexation, and ion exchange), and controlled by pH, ionic strength, solution speciation, mineral composition, organic matter, biological organisms, and temperature (see Section 6.3.1). 

Evaluation of spectroscopic data and ionic-strength dependence to guide the selection of divalent cation sorption reactions at low to moderate coverage where mononuclear sorption is the dominant reaction process. 

As sorption of organic phosphates occurs on surfaces with variable charges, the process is affected by the characteristics of the bulk solution, including pH, ionic strength, the nature and concentration of electrolytes, and... 

The potential errors in the use of Eqs. 1 and 2 result from the following facts retention of solutes, especially pro-tonated bases, by processes other than solvophobic interactions, e.g., with exposed silanols or metal contaminants change in values as a function of ionic strength solvophobic effect of ionic strength on solute retention ion-pair interaction of sample ions with ionized buffer species change in the sorption properties of the stationary phase (Cg or Clg) as a result of changing ionization of silanols a... 

As the system becomes more complex the applicability of adsorption isotherms and ion exchange models becomes inadequate. Surface complexation models offer a more universal description of the sorption process by taking into account important variables affecting sorption processes such as pH, ionic strength and aqueous speciation. This chapter provides an overview of the SCMs more detailed explanations of the derivations of these models can be found in geochemistry and environmental geochemistry textbooks such as those by Langmuir [14] and Benjamin [41]. Assumptions made in these models are ... 

---