INTRODUCTION
Chromatography
is a powerful analytical tool because it can be used to separate complex
mixtures. Why is this important? Because even sophisticated detection
techniques are most definitive when used to identify single, pure components.
With mixtures, identification becomes problematic. To better understand how chromatography
techniques work, this presentation is centered on the basic concepts in chromatography.
is a powerful analytical tool because it can be used to separate complex
mixtures. Why is this important? Because even sophisticated detection
techniques are most definitive when used to identify single, pure components.
With mixtures, identification becomes problematic. To better understand how chromatography
techniques work, this presentation is centered on the basic concepts in chromatography.
Chromatography can be defined as the
separation of components of a mixture by difference in partitioning or
distribution between two phases [1]. For example, liquid/liquid chromatography
could be used to separate components of a mixture based on their polarity. If
you wanted to identify a non-polar organic contaminate mixed with a polar
material, a simple way to separate them would be to add the mixture to a
container of oil and water and shake it. On the principle that like dissolves
like, the non-polar material would partition into the oil; the polar material
would move into the water. Once the oil and water phases separated, the water
phase could be removed, fresh water added, and the process of washing the oil
phase repeated until essentially all of the polar material was removed. The
purified non-polar contaminant in the oil phase could then be analyzed and
identified. The technique could be reversed to identify a polar component. The
concept of chromatography, as it is generally applied today, involves the
partitioning of mixtures between a stationary phase (the sorbent) and the mobile
phase (a liquid or gas).
separation of components of a mixture by difference in partitioning or
distribution between two phases [1]. For example, liquid/liquid chromatography
could be used to separate components of a mixture based on their polarity. If
you wanted to identify a non-polar organic contaminate mixed with a polar
material, a simple way to separate them would be to add the mixture to a
container of oil and water and shake it. On the principle that like dissolves
like, the non-polar material would partition into the oil; the polar material
would move into the water. Once the oil and water phases separated, the water
phase could be removed, fresh water added, and the process of washing the oil
phase repeated until essentially all of the polar material was removed. The
purified non-polar contaminant in the oil phase could then be analyzed and
identified. The technique could be reversed to identify a polar component. The
concept of chromatography, as it is generally applied today, involves the
partitioning of mixtures between a stationary phase (the sorbent) and the mobile
phase (a liquid or gas).
Chromatography involves a sample (or sample extract)
being dissolved in a mobile phase (which may be a gas, a
liquid or a supercritical fluid). The mobile phase is then forced through an
immobile, immiscible stationary phase. The phases are chosen such
that components of the sample have differing solubilities in each phase. A
component which is quite soluble in the stationary phase will take longer to
travel through it than a component which is not very soluble in the stationary
phase but very soluble in the mobile phase. As a result of these differences in
mobilities, sample components will become separated from each other as they
travel through the stationary phase.
being dissolved in a mobile phase (which may be a gas, a
liquid or a supercritical fluid). The mobile phase is then forced through an
immobile, immiscible stationary phase. The phases are chosen such
that components of the sample have differing solubilities in each phase. A
component which is quite soluble in the stationary phase will take longer to
travel through it than a component which is not very soluble in the stationary
phase but very soluble in the mobile phase. As a result of these differences in
mobilities, sample components will become separated from each other as they
travel through the stationary phase.
Techniques such as H.P.L.C. (High Performance Liquid
Chromatography) and G.C. (Gas Chromatography) use columns –
narrow tubes packed with stationary phase, through which the mobile phase is
forced. The sample is transported through the column by continuous addition of
mobile phase. This process is called elution. The average rate at
which an analyte moves through the column is determined by the time it spends
in the mobile phase.
Chromatography) and G.C. (Gas Chromatography) use columns –
narrow tubes packed with stationary phase, through which the mobile phase is
forced. The sample is transported through the column by continuous addition of
mobile phase. This process is called elution. The average rate at
which an analyte moves through the column is determined by the time it spends
in the mobile phase.
DISTRIBUTION OF ANALYTES
BETWEEN PHASES
BETWEEN PHASES
The distribution of analytes between phases can often be
described quite simply. An analyte is in equilibrium between the two phases;
described quite simply. An analyte is in equilibrium between the two phases;
Amobile