Chromatography - Equipment
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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
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
On to basic operation
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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.
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.