Electrokinetic method

Analysis of Grape and Wine Proteins and Peptides 7.3.1. Electrokinetic Methods 

Electrokinetic methods certainly comprise some of the most powerful techniques for protein analysis. They are based on the property of charged molecules to migrate in an electric field according to their net charge (isoelectric focusing, IEF), net charge and size (native electrophoresis) or only size (SDS-PAGE). These techniques include both analytical and preparative systems. 

These methods can be performed in slab gels (Polyacrylamide Gel Electrophoresis, PAGE) or in capillaries (Capillary Electrophoresis, CE). 

Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) 

Soaking the gel in fixing solution (50% methanol, 12% acetic acid and 0.05% formaldehyde) for 12 h 

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Unfortunately, we do not have microinterface voltmeters, and we can use only indirect methods like various chemical probes and electrokinetic methods. These methods make it possible to estimate only part of the Galvani potential, denoted here Aj[Pg.35]

Apart from paints, electrokinetic separations find limited application for synthetic polymers [905], mainly because of solvent compatibility (CE is mostly an aqueous technique) and competition of SEC (reproducibility). Reasons in favour of the use of CE-like methods for polymer analysis are speed, sample throughput and low solvent consumption. Nevertheless, CE provides some interesting possibilities for polymer separation. Electrokinetic methods have been developed based on differences in ionisation, degree of interaction with solvent constituents, and molecular size and conformation. 

The objective of comparing values of f determined from electrophoresis with those determined by other electrokinetic methods was stated at the beginning of Section 12.6. Enough experiments have been conducted in which at least two of the electrokinetic methods we have discussed are compared to leave no doubt as to the self-consistency of f as determined by these different methods. There is no guarantee, however, that self-consistent f potentials are correct. Consistency means only that f has been extracted from experimental quantities by a self-consistent set of approximations. It should be emphasized, however, that the existence of a potential at the surface of shear —which is the common component in all the electrokinetic analyses we have discussed —is more than amply confirmed by these observations. 

The major advantage of protein adsorption studies on high surface area materials is that changes of some extensive properties which accompany the process of adsorption are large enough to be directly measured heat of adsorption through microcalorimetry 141), uptake or release of small ions by a combination of electrokinetic methods and titration 142), thickness of adsorbed layer or an increase of the volume fraction of solid phase by a hydrodynamic method like viscometry 143). Chromatographiclike analysis can also be applied to protein adsorption 144). 

Electrokinetic methods are often in situ and involve inserting the electrodes directly into contaminated soils and sediments. When activated, the electrodes dissociate water, which produces oxidizing conditions and an acid front (perhaps at pH < 2) at the positively charged anode (Acar and Alshawabkeh, 1993, 2638) ... 

Electrokinetic method Refers to an in situ, and sometimes an ex situ, technology that removes contaminants from wet soils and sediments by passing electric currents through them. Unlike in situ vitrification, the currents in electrokinetic methods are too low to melt the materials. Instead, the electric currents cause contaminant ions and charged particles in aqueous solutions within the solid materials to migrate towards the electrodes, where they may be collected or otherwise treated. 

In sample introduction for CGE separation of oligonucleotides, hydro-dynamic method cannot be used, and an electrokinetic method must be used. Why (2 marks)... 

Abstract Investigations of alternate adsorption regularities of cationic polyelectrolytes a) copolymer of styrene and dimethylaminopropyl-maleimide (CSDAPM) and b) poly(diallyldimethylammonium chloride) (PDADMAC) and anionic surfactant - sodium dodecyl sulfate (SDS) on fused quartz surface were carried out by capillary electrokinetic method. The adsorption/desorption kinetics, structure and properties of adsorbed layers for both polyelectrolytes and also for the second adsorbed layer were studied in dependence on different conditions molecular weight of polyelectrolyte, surfactant and polyelectrolyte concentration, the solution flow rate through the capillary during the adsorption, adsorbed layer formation... 

In this paper we investigate the process of alternate adsorption of cationic polyelectrolyte and anionic surfactant, structure and properties of adsorbed layers depending on different factors (molecular weight of PE, concentration of polyelectrolyte and surfactant, adsorbed layer formation time, the flow rate of the solution) by measuring potential and streaming current using the capillary electrokinetic method. 

Electrokinetic measurements. In this study the capillary electrokinetic method was applied [16],... 

The capillary electrokinetic method allows to get the information about the structure of the adsorbed layers by measuring the dependence of f potential on the pressure enclosed (AP) (Figs. 6 and 7). 

The structure electrical double layer at the silica-aqueous electrolyte interface was one of the earlier examined of the oxide systems. At the beginning the investigations were performed with application of electrokinetic methods next, with potentiometric titrations. The properties of this system were very important for flotation in mineral processing. Measurements proved that pHpZC and pHiep are equal to 3, but presence of some alkaline or acidic contaminants may change the position of these points on pH scale. Few examples, concerning edl parameters are shown in Table 3. Presented data concern a group of systems of different composition of the liquid phase and solid of a different origin. The latest measurements of this system takes into account the kinetics of the silica dissolution [152], and at zeta measurements, also the porosity of dispersed solid [155]. 

Electrokinetic methods capillary electrophoresis (CE), micellar electrokinetic chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC), capillary electrochromatography (CEC)... 

Table 8.3 Electrokinetic methods for analysis of drug impurities...

One would perhaps expect that the hydrod3mamlc and electrokinetic methods measure the same thickness. This is in general not true, however. Contributions to the electrokinetic flux are located exclusively in the electrical double layer (i.e., up to distance of order x ) where the hydrodynamic flux is strongly Impeded by the adsorbed polymer. Also, since the extension of the electrical double layer is variable with the location d of the electrokinetic slip... 

Electroosmosis and electrophoresis are electrokinetic methods that are being considered for contaminated soil remediation." The principle behind these... 

Determination of the isoelectric point by electrokinetic methods is simple. The accuracy depends on control of the conditions such as pH and in the case of electrophoresis, on the positioning of the stationary layer [5,37]. A shortcoming of common methods is that one cannot characterise conductive samples. 

The method was extended for the materials whose PZC falls at very low pH values, where classical electrokinetic methods fail, and the CIP cannot be observed. For such material a linear relationship between tKL+ and pH over the pH range s4-7 was observed. Extrapolation of this straight line to k+ =0.5 gives the PZC. The data points obtained for low pH values show substantial deviations from linearity and they are not used in this extrapolation. 

C potentials, but no data points in the vicinity of the lEP are also presented. The lEP values for the same materials reported in other publications are presented in Tables 3.1 and 3.3. Organization of Table 3.9 is similar to the organization of Tables 3.1 and 3.3, and the method column is left empty when only classical electrokinetic methods were used. Table 3.9 substantiates the result obtained in Section I.C that the average of PZC values reported for quartz falls at lower pH than for silica gels, namely, in many studies only negative ( potentials of quartz are reported. 

Fig, 3,6), higher uptake, and/or higher ao. When uptake of the anion and the cation was studied, the formula of the salt is given in the column adsorbate . When only uptake of one of these ions was studied, the formula of the other ion is given in the column electrolyte . Table 3.10 reports also experimental conditions, namely, the solid to liquid ratio and equilibration time. The abbreviation in the column method is used for classical electrokinetic methods as opposite to the... 

A few PZCs reported in [1] (and quoted after [1]) were obtained by methods other than titration or electrokinetic methods. The principles of these methods were not described in detail, but names such as suspension effect, by adsorption of Zn and Co, and minimum gelation rate suggest that these PZCs do not meet the standards recommended in the present book, and such results are ignored in Chapter 3. On the other hand, a few PZCs obtained by means of the drift method cited after [1] are cited as such in Chapter 3. 

Instant coagulation also excludes methods that require a stable dispersion, such as electrophoresis. The manufacturers of certain types of zetameters claim that their instruments are suitable to perform measurements in electrolyte solutions up to about 1 M. However, in order to use a zetameter, one has to prepare a stable dispersion first, and this may be problematic. Electro-osmosis does not require stability against sedimentation, but other problems, such as low absolute values of the potential (which may be smaller than the scatter of results) and the production of heat, convective currents, or electrolysis products (acids, bases, and gases), severely limit the application of classical electrokinetic methods (including electrophoresis) in measurements at ionic strengths greater than 0.1 M. Very few publications report potentials obtained by classical electrokinetic methods at higher electrolyte concentrations, and the results are controversial. 

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