Instant Notes: Analytical Chemistry

Section D – Separation techniques

D2 PRINCIPLES OF

CHROMATOGRAPHY

Chromatography was originally developed by the Russian botanist Michael

Tswett in 1903 for the separation of colored plant pigments by percolating a

petroleum ether extract through a glass column packed with powdered calcium

carbonate. It is now, in general, the most widely used separation technique in

analytical chemistry having developed into a number of related but quite

different forms that enable the components of complex mixtures of organic or

inorganic components to be separated and quantified. A chromatographic

Chromatographic
separations

Key Notes

Chromatography is the process of separating the components of mixtures

(solutes) that are distributed between a stationary phase and a flowing

mobile phase according to the rate at which they are transported through

the stationary phase.

Solutes migrate through a stationary phase at rates determined by their

relative affinities for each phase, and are characterized by defined

retention parameters.

During a chromatographic separation, solute species are continually

transferred back and forth between the mobile and stationary phases by

the process of sorption followed by desorption. Several mechanisms by

which this occurs give rise to different modes of chromatography.

Individual solutes migrating through a stationary phase develop an

approximately symmetrical band or peak profile which becomes broader

as a function of time and distance travelled.

Peak profiles are fundamentally symmetrical but can become

asymmetrical, or skewed, as solutes migrate, due to changes in sorption

behavior.

The quality of a chromatographic separation is measured in terms of the

degree of band broadening, or efficiency, measured for individual peaks,

and the degree of separation, or resolution, of adjacent peaks.

Chromatographic analysis can provide qualitative information in terms

of characteristic retention parameters and quantitative information in

terms of peak areas or peak heights.

Related topics Thin-layer chromatography (D3) High-performance liquid

Gas chromatography: principles and chromatography: principles

instrumentation (D4) and instrumentation (D6)

Chromatographic

separations

Solute migration

and retention

Sorption processes

Peak profiles and

peak broadening

Peak asymmetry

Efficiency and

resolution

Qualitative and

quantitative analysis