Electrophoretic measurements

The inhibition of Streptococcus mutans adherence to hydroxyapatite with combinations of alkyl phosphates and nonionic surfactants was tested. Seven alkyl phosphate derivatives and three nonionic surfactants were examined for their ability to inhibit the adherence of 3H-labeled cells of S. mutans to hydroxyapatite treated with buffer or parotid saliva. No compound by itself effectively hindered binding of bacteria to hydroxyapatite. A combination of certain of the alkyl phosphates, notably a disodium phosphate of 1-octadecanol, and nonionic surfactant at a 1 1 molar ratio gave a strong inhibition of S. mutans adherence. Treatment with this combination resulted in 98% reduction of adherence. Adsorption of the two types of surface-active agents alone and in combinations was studied using 14C-labeled agents. Electrophoretic measure-... 

An important reason for this lack of experimental work is that the zeta-potential cannot be easily determined independent of the electrophoretic mobility [284] however, in the case of proteins (as well as some other charged colloids), the intrinsic charge obtained by titration is a parameter that can be measured independent of the electrophoretic mobility. The charge obtained from electrophoretic measurements (i.e., the net charge) via the preceding theories is generally not the same as the charge obtained from titration (i.e., the in-... 

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. 

The surface potential is not accessible by direct experimental measurement it can be calculated from the experimentally determined surface charge (Eqs. 3.1 - 3.3) by Eqs. (3.3a) and (3.3b). The zeta potential, calculated from electrophoretic measurements is typically lower than the surface potential, y, calculated from diffuse double layer theory. The zeta potential reflects the potential difference between the plane of shear and the bulk phase. The distance between the surface and the shear plane cannot be defined rigorously. 

There is no experimental way to measure y. (As we mentioned before, the zeta potential - as obtained, for example, from electrophoretic measurments - is in a not readily definable way - smaller than y.) But as discussed in section 3.3 we can obtain the surface charge (Eq. 3.2) and then compute the surface potential y on the basis of the diffuse double layer model with Eq. (3.8a) Eq. (3.8a) in simplified form for 25° C is... 

Materials. Synthetic hematite was obtained from J. T. Baker Chemical Company, Phillipsburg, NJ. Particle size analysis using a HIAC instrument (Montclair, CA) indicated the particles to be 80 percent (number) finer than 2 microns. Using nitrogen as the adsorbate, the B.E.T. specific surface area was found to be 9 square meters per gram. The point of zero charge, as obtained from electrophoretic measurements in the presence of indifferent electrolytes, occurred at pH 8.3. 

The disjoining pressure vs. thickness isotherms of thin liquid films (TFB) were measured between hexadecane droplets stabilized by 0.1 wt% of -casein. The profiles obey classical electrostatic behavior. Figure 2.20a shows the experimentally obtained rt(/i) isotherm (dots) and the best fit using electrostatic standard equations. The Debye length was calculated from the electrolyte concentration using Eq. (2.11). The only free parameter was the surface potential, which was found to be —30 mV. It agrees fairly well with the surface potential deduced from electrophoretic measurements for jS-casein-covered particles (—30 to —36 mV). 

In the above equations, h is the film thickness, n is the munber concentration of z z symmetrical electrolyte and is the surface potential. The surface potential is the potential at the interface of stem and diffuse layers and is usually replaced by the zeta potential of the droplet determined from electrophoretic measurements. When the interface has an adsorbed layer of globular proteins, it may be reasonable to assume that the shear plane is located at the interface of protein layer. When xp > 2L, the disjoining pressure 11 / can be evaluated by replacing with potential and taking as (jCf - 2L,). 

The glass beads used in this work were too large for electrophoretic measurements and therefore it was not possible to carry out mobility experiments with them. 

The surface of uncalcined aluminas consists of amphoteric hydroxyl groups that are even less acidic than those in silica gel. Electrophoretic measurements by Stigter et al. (90) show that the isoelectric point for alumina is attained at a pH of 9, much higher-than the value of 2 obtained in the case of silica gel. Thus, hydroxylated aluminas are relatively non-acidic, unless they are promoted with acid-producing impurities. 

We are unable so far to explain the systematic difference in surface potential and density estimates from the two methods. Our numbers decrease if we assume that charge binds some distance into the water away from the bilayer surface (JO), but this distance must be an improbable 16 A to achieve reconciliation with the electrophoretic measurements. Conversely, the electrophoretic slip plane for the zeta potential would have to be an unlikely 16 A away from the actual locus of charge... 

J. Wang, G. Chen and M.P. Chatrathi, Nickel amperometric detector prepared by electroless deposition for microchip electrophoretic measurement of alcohols and sugars, Electroanalysis, 16 (2004) 1603-1608. 

Electrophoretic measurements by the microscope method are complicated by the simultaneous occurrence of electro-osmosis. The internal glass surfaces of the cell are usually charged, which causes an electro-osmotic flow of liquid near to the tube walls together with (since the cell is closed) a compensating return flow of liquid with maximum velocity at the centre of the tube. This results in a parabolic distribution of liquid speeds with depth, and the true electrophoretic velocity is only observed at locations in the tube where the electro-osmotic flow and return flow of the liquid cancel. For a cylindrical cell the stationary level is located at 0.146 of the internal diameter from... 

The wall of a fused silica capillary, containing silanol groups, has been identified as a potential site of interaction for solutes in electrophoretic measurements. In particular, adsorption of proteins, peptides and other basic compounds has been more specifically addressed [1-3]. In the ideal situation, the interaction is strictly chromatographic so that the process is reversible with the net result being a loss in the observed efficiency for CE [2,4]. A more serious problem can result when there is irreversible adsorption of the analyte on the capillary wall leading to a lack of repro-... 

The electrostatic stabilization theory was developed for dilute colloidal systems and involves attractive van dcr Waals interactions and repulsive double layer interactions between two particles. They may lead to a potential barrier, an overall repulsion and/or to a minimum similar to that generated by steric stabilization. Johnson and Morrison [1] suggest that the stability in non-aqueous dispersions when the stabilizers are surfactant molecules, which arc relatively small, is due to scmi-stcric stabilization, hence to a smaller ran dcr Waals attraction between two particles caused by the adsorbed shell of surfactant molecules. The fact that such systems are quite stable suggests, however, that some repulsion is also prescni. In fact, it was demonstrated on the basis of electrophoretic measurements that a surface charge originates on solid particles suspended in aprotic liquids even in the absence of traces of... 

Acknowledgment. We are indebted to Prof. M. Ettinger for performing the nondenaturating electrophoretic measurements on apoferritin and to Prof. G. Frens for drawing our attention to the experimental results discussed in ref 8. 

It follows from the discussion above that knowledge of both k" and k" is required to assess the chromatographic and electrophoretic contributions to migration of charged sample components in CEC. However, both of them cannot be determined from CEC data alone and require electrophoretic measurements, as described above. 

With electro-osmosis data, on the other hand, interpretation is not subject to the complexities of the electrophoretic measurement. Analysis of zeta potential is straightforward, and a wide range of pH can be employed. In this light it would be promising to characterize ceramic and mineral materials of a wide variety of compositions and forms, e.g., powders and processed plates. 

Dielectric and electrophoretic measurements supported the hypothesis that zwitterions were formed. Electrophoretic mobility could be demonstrated for a polymer sample after its esterification with methyl iodide. 

A contemporary study by Jayson et al. [307] does cite the paper by Muller et al. [523] and thus combines electrophoretic measurements on an activated carbon cloth (ACC, pHipp = 2.7) with the analysis of pH effects on uptakes of triethyl and dimethyl (pK = 2.12) phosphates. Table 22 summarizes the Langmuir monolayer capacities obtained in an effort to unravel the controlling mechanisms governing adsorption of these pesticides. While the low values of adsorption heats (<5 kJ/mol) suggested that the ad.sorption process is purely physical... 

The data obtained on various proteins of moderate asymmetry are reported in Table 2. It should be noted that the zein preparations are highly polydispersed the others, while for the most part not strictly monodispersed, are fairly uniform, consisting chiefly of a single component, by ultracentrifugal and electrophoretic measurements, except for hemocyanin, which exists in three different sizes, as indicated. Sedimentation, diffusion and viscosity measurements have been carried out on all of these proteins and in general the agreement between the different methods is reasonabty satisfactory. 

The adsorption and electrophoretic measurements were supplemented by the qualitative observation of the flocculation of solid particles in the surfactant solutions. The turbidity of the content of each adsorption tube after adsorption, recorded at various time intervals, was compared with that of a control tube containing the same solid concentration but in pure solvent. This suspension of reference was always prepared under the same conditions as the others. A marked increase in the turbidity was taken as evidence of flocculation. 

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