Fundamentals

Electrophoretic Migration of Ions

The uniform motion of an ion under an electric field can be recognized as a result of balancing electromotive and frictional forces of the ion in solution:

where q is the effective charge of the ion concerned, E is electric field, while r is the ion's Stokes radius, r is the dynamic viscosity of the solution, and u is the linear velocity of the ion. The important parameter, electrophoretic mobility (u), is defined as the ion's

Figure 1 Capillary zone electrophoresis separation of fluor-escamine-labelled peptides obtained from a tryptic digest of reduced and carboxymethylated egg white lysozyme. (Adapted with permission from Jorgenson JW and Lukacs KD (1981) Zone electrophoresis in open-tubular glass capillaries: preliminary data on performance. Journal of High Resolution Chromatography and Chromatographic Communications 4: 230 -231.)

Figure 1 Capillary zone electrophoresis separation of fluor-escamine-labelled peptides obtained from a tryptic digest of reduced and carboxymethylated egg white lysozyme. (Adapted with permission from Jorgenson JW and Lukacs KD (1981) Zone electrophoresis in open-tubular glass capillaries: preliminary data on performance. Journal of High Resolution Chromatography and Chromatographic Communications 4: 230 -231.)

linear velocity per unit of electric field:

fixed. Hence electrophoretic mobility, the inherent attribute of an ion is directly reflected by its migration time. This provides the theoretical basis of using migration time as a means of identifying an ion in CE.

Electroosmotic Flow (EOF)

Electroosmosis is a fundamental electrokinetic effect involving movement of the bulk solution against a charged solid surface under the influence of an electric field. In the case of CE, the capillary inner wall usually carries negative charges due to the de-protonation of silanol groups. For the part of the liquid adjacent to the capillary wall, build-up of cations takes place to counterbalance the negative charges on the capillary surface. According to Stern's double layer model the solution containing net cations can be divided into two regions, namely a rigid layer and a diffuse double layer. The rigid layer is immediately adjacent to the capillary wall, so the cations within it are largely immobilized owing to the strong electrostatic interaction with the wall. The diffuse layer is slightly away from the wall, hence the cations inside are mobile. Upon the application of a voltage, these cations together with their surrounding hydrating water will migrate towards the cathode. The cohesive nature of water causes the whole solution inside the capillary to be dragged forward, generating a net flow across the capillary. This is named the electroosmotic flow (EOF). The magnitude of the EOF can be described via the Helmultz equation:

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment