Chromatography

CHEMISTRY 1000

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Chromatography

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

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 ion-exchange chromatography – the experiment.

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Liquid Chromatography

Separates ions based on polarity. Two techniques:

Normal phase: stationary phase is a polar solid while the mobile phase is a less polar

liquid.

example: silica as stationary phaseand ether/hydrocarbon mixtureas mobile phase

Reverse phase: stationary phase is nonpolar while the mobile phase is more polar.

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Liquid Chromatography

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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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):

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.

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: Environmental analyses Identifying illicit

substances Explosives detection Medical applications

Gas Chromatography (GC and/or GC/MS)