Saturday, March 21, 2009

Chromatography - Equipment

The Column
Although there are other types of chromatography (e.g. paper and thin layer), most modern applications of chromatography employ a column. The column is where the actual separation takes place. It is usually a glass or metal tube of sufficient strength to withstand the pressures that may be applied across it. The column contains the stationary phase. The mobile phase runs through the column and is adsorbed onto the stationary phase. The column can either be a packed bed or open tubular column.

Packed Bed Column
A packed bed column is comprised of a stationary phase which is in granular form and packed into the column as a homogeneous bed. The stationary phase completely fills the column.

Open Tubular Column
An open tubular column's stationary phase is a thin film or layer on the column wall. There is a pasageway through the center of the column.

The Mobile and Stationary Phases

The mobile phase is comprised of a solvent into which the sample is injected. The solvent and sample flow through the column together; thus the mobile phase is often referred to as the "carrier fluid." The stationary phase is the material in the column for which the components to be separated have varying affinities. The materials which comprise the mobile and stationary phases vary depending on the general type of chromatographic process being performed.

Gas Chromatography
The mobile phase in gas chromatography is generally an inert gas. The stationary phase is generally an adsorbent or liquid distributed over the surface of a porous, inert support.

Liquid Chromatography
The mobile phase in liquid chromatography is a liquid of low viscosity which flows through the stationary phase bed. This bed may be comprised of an immiscible liquid coated onto a porous support, a thin film of liquid phase bonded to the surface of a sorbent, or a sorbent of controlled pore size.

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