Ionic strength adsorption constant

An important component of compoimding is the consideration of factors influencing the stability of the hnal prepararion. These factors include pH, temperature, solvent, light, air (oxygen, carbon dioxide, moisture), humidity, particle size, ionic strength, dielectric constant, polymorphism, crystallizarion, vaporization, and adsorption. 

Figure 3.2 shows the electrokinetic potential of a material as a function of the pH for different concentrations of inert electrolyte. Such plots are typical for simple and mixed (hydr)oxides and for many salts whose surface charging is pH dependent (Section 3.I.G). The increase in the ionic strength at constant pH depresses the absolute value of C potential, but the lEP is not affected. The electrokinetic curves in the presence of inert electrolytes are nearly symmetrical with respect to the pristine lEP (Figs. 3.84-3.100), when the electrolyte concentration is not too high. Very high concentrations of 1-1 electrolytes (>0.I mol dm ) induce effects characteristic for specific adsorption of cations, i.e. 

Determination of the extent of adsorption at various pH values and constant ionic strength (adsorption edge)... 

Pullerits et al.m studied specific adsorption of I from an aqueous solution at constant ionic strength. 

Table 3. Representative affinity constants for the binding of metal to transport sites or whole cells/organisms. Ionic strengths and pH values are given for the conditional constants. In the column Comments , information on the method of determination (Km = Michaelis-Menten constant WC = whole-cell titrations) the type of constant (CC = conditional constant IC = intrinsic constant) and special conditions (Cl = competitive inhibitors NICA = nonideal competitive adsorption) are given...

Proteins contain a variety of functional groups and interact with the stationary phase at a number of simultaneous sites on the protein molecule, each more or less affected by change in eluent, or mobile-phase, pH or ionic strength. The equilibrium constant for the dissociation of the adsorption complex thus contains a product of many eluent-sensitive concentration terms, and the equilibrium position is very sensitive to elution conditions. Under the elution conditions, some proteins in a mixture may be tightly bound by the stationary phase (t), oo) while others are unretained (t R 0). Differential migration (Section 19.2.1) is replaced by extreme retention values. 

Fusions to thermostable enzymes will allow us to evaluate adsorption at higher temperatures. When a column containing Abg-CBDcex/ adsorbed to cellulose at pH 7.0, was eluted with an increasing or decreasing pH gradient (constant ionic strength), protein (enzymatically inactive) was eluted above pH 9, but there was no desorption evident at low pH. (Ong, E. Gilkes, N.R Miller, R.C., Jr. Warren, R.A.J. Kilbum, D.G. Enzyme Microb, TechnoL, in press). 

Figure 2.22. (a) Disjoining pressure vs. thickness isotherm for an emulsion film stabilized by 0.1% BSA, ionic strength of 10 mol/1 NaCl, oil phase = hexadecane. The dots are the experimental data, dashed line is the double-layer contribution to the total disjoining pressure, and the solid line is the best fit done supposing additivity of the double-layer and steric forces, (b) Force vs. distance profiles for ferrofluid emulsions stabilized with mixed BSA-Tween-20 adsorption layers. The total concentration of the Tween-20 is kept constant = 5CMC, pH = 5.8. (Adopted from [78].)... 

Some stability constants for ion pairs on Fe oxides are listed in Table 10.4. This model was applied by Davis and Leckie (1978, 1980) to adsorption of various cations and anions on ferrihydrite. The extended triple layer model of Sahai and Svenjensky (1997) incorporates recent advances in aqueous electrolyte chemistry which enable aqueous activity coefficients for electrolytes to be calculated over a wide range of ionic strengths. The model also considers the free energy of adsorption of an ion to be the sum of the contributions from an electrostatic term, a Born solvation term and a ion intrinsic term. This extended model has been applied to adsorption of Co and Cd on goethite. 

The Helmholtz-von Smoluchowski equation indicates that under constant composition of the electrolyte solution, the EOF depends on the magnitude of the zeta potential, which is determined by various factors inhuencing the formation of the electric double layer, discussed above. Each of these factors depends on several variables, such as pH, specihc adsorption of ionic species in the compact region of the double layer, ionic strength, and temperature. 

Surface Adsorption. From Fig.l and Fig.2 we can calculate the total surface adsorption (17 ) of the RDH-surfac-tant mixture by applying the Gibbs adsorption equation(7). In the case of a mixed aqueous solution with a constant ionic strength, the equation is written as... 

In order to elucidate the effect of alkyl alcohol on the surface adsorption of CyFNa and C,oSNa, it is useful to calculate the surface molecular interaction parameters of the binary surface active mixtures (y8,) according to the equation at constant surface tension and constant ionic strength (13,14,10) ... 

For the surface adsorption of binary mixed solution at a constant ionic strength, the Gibbs equation is (6)... 

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