Chromatography
Vacuum distillation should be used if the boiling points are over 150°C to prevent degradation of
the product.
Fractional distillation should be used if the boiling points are less than 25°C apart because it
allows more refined separation of liquids by boiling point.
All forms of chromatography use two phases to separate compounds based on physical or
chemical properties.
The stationary phase or adsorbent is usually a polar solid.
The mobile phase runs through the stationary phase and is usually a liquid or gas. This elutes
the sample through the stationary phase.
Compounds with higher affinity for the stationary phase have smaller retardation factors and
take longer to pass through, if at all; compounds with higher affinity for the mobile phase elute
through more quickly. Compounds therefore get separated from each other, called
partitioning.
Thin-layer and paper chromatography are used to identify a sample.
The stationary phase is a polar material, such as silica, alumina, or paper.
The mobile phase is a nonpolar solvent, which climbs the card through capillary action.
The card is spotted and developed; Rf values can be calculated and compared to reference
values.
Reverse-phase chromatography uses a nonpolar card with a polar solvent.
Column chromatography utilizes polarity, size, or affinity to separate compounds based on their
physical or chemical properties.
The stationary phase is a column containing silica or alumina beads.
The mobile phase is a nonpolar solvent, which travels through the column by gravity.
In ion-exchange chromatography, the beads are coated with charged substances to bind
compounds with opposite charge.
In size-exclusion chromatography, the beads have small pores which trap smaller
compounds and allow larger compounds to travel through faster.
In affinity chromatography, the column is made to have high affinity for a compound by
