Instant Notes: Analytical Chemistry

Section D – Separation techniques

D8 ELECTROPHORESIS AND

ELECTROCHROMATOGRAPHY:

PRINCIPLES AND

INSTRUMENTATION

Principles Electrophoresis, in its classicalform, is used to separate mixtures of charged
solute speciesby differential migration through a buffered electrolyte solution
supported by a thin slab or short column of a polymeric gel, such as polyacry-

Key Notes

Electrophoresis is a technique for the separation of components of

mixtures by differential migration through a buffered medium across

which an electric field is applied. Electrochromatography is a hybrid of

electrophoresis and HPLC.

Samples are introduced into a buffer solution that provides an electrically

conducting medium and pH stability throughout the separation.

In some modes of electrophoresis, solutes migrate through a solid

medium consisting of a polymeric gel which supports the running buffer.

The application of a potential gradient across the running buffer causes

hydrated buffer cations to move towards the cathode. The resulting bulk

flow of liquid is described as an electro-osmotic flow, and is of particular

significance in high-performance capillary electrophoresis.

Samples are placed in wells formed in the gel slab or column, or

introduced into a capillary column by hydrodynamic or electrokinetic

means.

Solutes are either all detected in situafter the separation is complete by

treating the supporting medium with a chromogenic reagent, or

sequentially in the running buffer as they migrate towards one end of a

capillary tube.

A dedicated microcomputer is an integral part of a modern

electrophoresis system. Software packages facilitate the control and

monitoring of instrumental parameters, and the display and processing

of data.

Related topics Principles of chromatography (D2) High-performance liquid

chromatography: principles

and instrumentation (D6)

Principles

Running buffer

Supporting medium

Electro-osmosis

Sample injection

Solute detection

Instrument control

and data processing