Effective electrokinetic mobility

Electrokinetic (also called electromigration) injection is performed by placing the inlet of the capillary and an electrode in the sample vial. Following this a voltage is applied during a defined period of time. The sample constituents are actively carried into the capillary, and when present, the EOF also passively carries them into the capillary. For this reason, neutral compounds are also injected. The active migration is due to the effective electrophoretic mobilities of the constituents. The amount (B), in units of concentration injected into the capillary is expressed by [2,38]... 

The effects of inert electrolyte on surface charging of salts other than Agl are not very well documented. The electrokinetic mobility of two samples of calcite was... 

Electrokinetic Transport in Soil Remediation, Table 1 Diffusion, ionic mobility, and effective ionic mobility for selected cationic and anionic species. Effective mobility was calculated for porosity n = 0.6 and tortuosity t = 0.35 [1]... 

The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

Flow movement also has a relationship with the electrokinetic phenomenon, which can promote or retard the motion of the fluid constituents. Electrokinetic effects can be described as when an electrical double layer exists at an interface between a mobile phase and a stationary phase. A relative movement of the two phases can be induced by applying an electric field and, conversely, an induced relative movement of the two will give rise to a measurable potential difference.33... 

Two conditions must be met to justify comparisons between f values determined by different electrokinetic measurements (a) the effects of relaxation and surface conductivity must be either negligible or taken into account and (b) the surface of shear must divide comparable double layers in all cases being compared. This second limitation is really no problem when electroosmosis and streaming potential are compared since, in principle, the same capillary can be used for both experiments. However, obtaining a capillary and a migrating particle wiih identical surfaces may not be as readily accomplished. One means by which particles and capillaries may be compared is to coat both with a layer of adsorbed protein. It is an experimental fact that this procedure levels off differences between substrates The surface characteristics of each are totally determined by the adsorbed protein. This technique also permits the use of microelectrophoresis for proteins since adsorbed and dissolved proteins have been shown to have nearly identical mobilities. 

The first and most often encountered separation mechanism in CE is based on mobility differences of the analytes in an electric field these differences are dependent on the size and charge-to-mass ratio of the analyte ion. Analyte ions are separated into distinct zones when the mobility of one analyte differs sufficiently from the mobility of the next. This mechanism is exemplified by capillary zone electrophoresis (CZE) which is the simplest CE mode. A number of other recognized CE modes are variations of CZE. These are micellar electrokinetic capillary chromatography (MECC), capillary gel electrophoresis (CGE), capillary electrochromatography (CEC), and chiral CE. In MECC the separation is similar to CZE, but an additional mechanism is in effect that is based on differences in the partition coefficients of the solutes between the buffer and micelles present in the buffer. In CGE the additional mechanism is based on solute size, as the capillary is filled with a gel or a polymer network that inhibits the passage of larger molecules. In chiral CE the additional separation mechanism is based on chiral selectivity. Finally, in CEC the capillary is packed with a stationary phase that can retain solutes on basis of the same distribution equilibria found in chromatography. 

Fig. 8.15. Effect of particle diameter and pore diameter on the separation of 12 PTH-amino acids. Column, 150 x 0.075 mm i.d. packed with 6 pm/300 A or (b) 3.5 pm/80 A Zorbax ODS eluents, (A) 2 mmol/1 ammonium acetate, pH 7.0, (B) 2 mmol/1 ammonium acetate, pH 7.0, 90% acetonitrile gradient elution with 30- 90% B in 15 min flow rate of mobile phase through inlet reservoir, 100 pl/min applied voltage, 20 kV detection, ESI-MS, 0.5 s/spectrum integration time sheath liquid, 1 mmol/1 ammonium acetate, pH 7.0, 90% methanol, 3 pl/min injection, electrokinetic, 2 kV, 2 s sample, PTH-asparagine, PTH-glutamine, PTH-threonine, PTH-glycine, PTH-alanine PTH-tyrosine, PTH-valine, PTH-proline PTH-tryptophan, PTH-phenylalanine, PTH-isoleucine, PTH-leucine (in order of elution). (Reproduced from ref. [113] with permission of the author).

---