Electrophoretic mobility adsorption

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

It is interesting to compare these results with the electrophoretic measurements made under identical electrolyte concentrations. Figure 8 shows that the variation of electrophoretic mobility with sodium chloride concentration is different for the bare and the PVA-covered particles. For the bare particles, the mobility remains constant up to a certain salt concentration, then increases to a maximum and decreases sharply, finally approaching zero. The maximum in electrophoretic mobility-electrolyte concentration curve with bare particles has been explained earlier (21) by postulating the adsorption of chloride ions on hydrophobic polystyrene particles. In contrast, for the PVA-covered particles, the mobility decreases with increasing electrolyte concentration until it approaches zero at high salt concentration. 

TABLE 1 Electrophoresis of BSA adsorbed on glass at various ionic strengths. Initial adsorption (at 0.25% w/v, BSA) at 1.96 yg/cm2, and electrophoretic mobility U. 

Influence of the Surface Concentration of BSA. Compared to the corrected moving boundary electrophoretic mobility of BSA in solution, the mobility of BSA adsorbed onto glass is considerably faster at all ionic strengths at 1.96 pg/cm2 and somewhat faster at lower ionic strengths 1.38 pg/cm2. However, at lower adsorption densities (1.05 and 0.64 pg/cm2), the adsorbed BSA moves more slowly in the applied electric field than BSA in moving boundary electrophoresis under otherwise identical conditions, and at the lowest surface adsorption (0.64 pg/cm2) the mobility of the adsorbed BSA are even somewhat slower than in cellulose acetate gel at all conditions of ionic strength investigated. 

Figure 6.15 The effect of adsorption of polyethyleneimines of different molecular weight on electrophoretic mobility of cellulose (PEI 10 = DP of 10 and PEI 500 = DP of500 figures in brackets are negative).

Electrostatic vs. Chemical Interactions in Surface Phenomena. There are three phenomena to which these surface equilibrium models are applied regularly (i) adsorption reactions, (ii) electrokinetic phenomena (e.g., colloid stability, electrophoretic mobility), and (iii) chemical reactions at surfaces (precipitation, dissolution, heterogeneous catalysis). 

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

Figure 4. Influence of magnesium adsorption on the electrophoretic mobility of HAP at 37°C, 0.01 mol L 1 KNO3 background electrolyte ...

Electrokinetic Measurements. Electrophoretic mobilities were measured with a flat-cell apparatus manufactured by Rank Brothers, Cambridge, England. In addition, several mobility values were checked for accuracy with a Zeta Meter, New York. Mobilities were determined with a small volume of the suspension (approximately 25 cc) that had been prepared for the adsorption experiments. The pH of the solution was measured prior to determining the electrophoretic mobilities, which involved measuring the velocities of five to ten particles in each direction. An average value of the mobilities was recorded. Samples containing the flocculated particles were dipped into an ultrasonic bath for approximately one second prior to making the pH and mobility measurements. 

Figure 5. Electrophoretic mobility of hematite at pH 4.1 and 0.001 M NaCl as a function of sulfonate adsorption density in the absence and presence of pre-adsorbed polyacrylic acid.

The mechanism of interaction of amino acids at solid/ aqueous solution interfaces has been investigated through adsorption and electrokinetic measurements. Isotherms for the adsorption of glutamic acid, proline and lysine from aqueous solutions at the surface of rutile are quite different from those on hydroxyapatite. To delineate the role of the electrical double layer in adsorption behavior, electrophoretic mobilities were measured as a function of pH and amino acid concentrations. Mechanisms for interaction of these surfactants with rutile and hydroxyapatite are proposed, taking into consideration the structure of the amino acid ions, solution chemistry and the electrical aspects of adsorption. 

Only a few systematic studies have been carried out on the mechanism of interaction of organic surfactants and macromolecules. Mishra et al. (12) studied the effect of sulfonates (dodecyl), carboxylic acids (oleic and tridecanoic), and amines (dodecyl and dodecyltrimethyl) on the electrophoretic mobility of hydroxyapatite. Vogel et al. (13) studied the release of phosphate and calcium ions during the adsorption of benzene polycarboxylic acids onto apatite. Jurlaanse et al.(14) also observed a similar release of calcium and phosphate ions during the adsorption of polypeptides on dental enamel. Adsorption of polyphosphonate on hydroxyapatite and the associated release of phosphate ions was investigated by Rawls et al. (15). They found that phosphate ions were released into solution in amounts exceeding the quantity of phosphonate adsorbed. 

Below the PZC of Ti02 (pH < 6.7) adsorption of glutamic acid makes the electrophoretic mobility more negative as anticipated. At pH s... 

Outer-sphere adsorption of Pb(ll)EDTA on goethite. Geochim. Cosmochim. Acta 63(19/20) 2957-2969 Bargar, J.R. Reitmeyer, R. Davis, J.A. (1999) Spectroscopic confirmation of uranium(Vl)-carbonato adsorption complexes on hematite. Environ. Sci. Techn. 33 2481-2483 Bargar, J.R. Reitmeyer, R. Lenhart, J.J. Davis, J.A. (2000) Characterization of U(Vl)-car-bonato ternary complexes on hematite EX-AFS and electrophoretic mobility measurements. Geochim. Cosmochim. Acta 64 ... 

In addition, the composition of the electrolyte solution can strongly influence sample solubility and detection, native conformation of biopolymers, molecular aggregation, electrophoretic mobility, and EOF, which can be altered as a consequence of the adsorption of the components of the BGE onto the capillary wall. Consequently, selecting the proper composition of the electrolyte solution... 

The adsorption of Co(II) at the silica-water interface has been studied as a function of pH, ionic strength, and total Co(II) concentration. The adsorption data, together with electrophoretic mobility and coagulation data suggest that the free aquo Co(II) ion is not specifically adsorbed without participation of surface hydroxyls. Evidence for polymeric Co(OH)2 at the quartz surface is presented together with evidence of mutual coagulation of the quartz and precipitated cobalt hydroxide. 

To evaluate + for each metal ion, values of p8 are required at each concentration. While this can often be evaluated from electrophoretic mobility data, the high ionic strengths—Le., pH < 2—preclude meaningful measurement of mobilities. However, it can be seen that when ij/s and cf)+ are equal and opposite then adsorption is reduced to zero. The adsorption of Na+ is reduced to zero at the z.p.c. since, in this case, + is negligibly small. With Ni2+ and Cu2+ the pH must be reduced—i.e., made more positive—by 1.3 pH units to effect zero adsorption. Since near the z.p.c. ips and i//0, the total double layer potential, are approximately equal and given by the Nernst Equation, then... 

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