Principle Of Chromatography Essay

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The chromatography term is derived from a Greek word Chromo for color and Graphe for writing. Chromatography is a separation technique based on the partitioning behavior. The concept of chromatography was introduced by a Russian botanist Mikhail Tswett in 1906.
In this technique solute of interest is partitioned between two phases i.e. a mobile phase and a stationary phase depending on the partitioning value.
The mobile phase includes the solvent and the stationary phase includes the column in which the solvent is immobilized.
The techniques mainly depend on adsorption, partition, ion exchange or molecular exclusion.
The analyte is in equilibrium between the two phases and the distribution depends on the partitioning coefficient.
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the Height Equivalent to a Theoretical Plate (the smaller HETP narrower the eluted peak).
If the length of the column is L, then the HETP is
Where N is the number of theoretical plates
A chromatographic column can have millions of theoretical plates. The width of bands increases as the retention time (volume) increases.

This theory describes the actual process going on inside the chromatographic column with respect to the time taken for the solute to equilibrate between the stationary and mobile phase. The kinetic effect depends upon how much time the mobile phase spends in contact with the stationary phase.
The rate of elution affects the band shape of a chromatographic peak. It is also affected by the different paths available to solute molecules as they travel between particles of stationary phase.
The reason for band broadening was well explained by Van Deemter equation for plate height
HETP = A + B/u + Cu where u is the average velocity of the mobile phase.
A is the eddy diffusion. B is longitudinal

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