CHEMISTRY 1000
Chromatography
Chromatography
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Chromatography is a technique for separating species based on
physical or chemical properties.
Usually made up of the species to be separated, a stationary
phase, and a mobile phase.
Separation of different compounds depends on relative affinity of
the compounds for the stationary phase and the mobile phase.
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Ion-Exchange Chromatography
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Separates ions based on magnitude of charge (must all have the
same sign of charge.
Stationary phase usually consists of beads, whose surfaces are
covered with charged groups. Examples:
The mobile phase is a salt solution of progressively increasing
concentration.
Ions with larger charges are more strongly attracted to the
stationary phase and can displace ions with smaller charges.
To remove ions with largest charge, flush system with conc.
solution of another ionic compound.
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Ion-Exchange Chromatography
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ion-exchange chromatography – the experiment.
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Liquid Chromatography
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Separates ions based on polarity.
Two techniques:
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Normal phase:
stationary phase is a polar solid while the
mobile phase is a less polar liquid.
example: silica as stationary phase
and ether/hydrocarbon mixture
as mobile phase
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Reverse phase:
stationary phase is nonpolar while the mobile
phase is more polar.
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Liquid Chromatography
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More polar solutes are more strongly attracted to stationary
phase (stronger IMF).
Less polar solutes are less attracted to the stationary phase
(weaker IMF).
Therefore less polar species will travel faster through the
column than more polar species.
For given experimental conditions, the time for a species to
elute (move through the column) is highly reproducible.
High performance liquid chromatography (HPLC) is a widely
used type of liquid chromatography in which the mobile phase is
pressurized to push it through the stationary phase more
quickly.
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Gas Chromatography (GC and/or GC/MS)
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Stationary phase is a viscous liquid coated on the inside of a
thin tube called a column.
Mobile phase is an inert gas.
Separates ions based on boiling point (IMF):
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substances with higher boiling point spend more time in the
stationary phase (stronger IMFs result in longer retention in the
stationary phase).
boiling point increases with stronger IMFs.
Molecules in the gas can become dissolved in the stationary
phase, slowing their progress through the column.
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Gas Chromatography (GC and/or GC/MS)
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Chromatography is used to
separate mixtures.
When used with Mass
Spectrometry (MS) this can be
a powerful technique to
separate (purify) and identify
compounds.
Applications:
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Environmental analyses
Identifying illicit substances
Explosives detection
Medical applications
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