Different methods are used to separate different mixtures. The method chosen depends upon the properties of the components of the mixture.
|Separation method||Suitable for separating:|
|Filtration||An insoluble solid from a liquid|
|Crystallisation||A soluble solid from a solution|
|Simple distillation||A solvent from a solution|
|Fractional distillation||One or more liquids from a mixture of liquids|
|Chromatography||Coloured soluble substances|
In this chromatogram, brown ink is made of a mixture of red, blue and yellow substances. This is because the coloured substances in the brown ink travel the same distances (and have the same Rf values) as the reference substances.
In gas chromatography (GC):
The stationary phase is held on an unreactive solid support such as silica beads. These are packed into a long, coiled ‘column’ inside a thermostatically-controlled oven. A detector measures the amount of each substance in a mixture as it leaves the column:
The GC machine plots a graph of detector reading against retention time. Three main pieces of information can be gathered from a gas chromatogram:
This gas chromatogram shows that: