Explain how chromatography is used to separate components in a mixture.
Chromatography separates components in a mixture according to their solubility in the mobile phase and their adsobance to the stationary phase. The mobile phase is the part of the chromatography set up that moves; the stationary phase is the part of the set up that does not move.
Components that are more soluble in the mobile phase, i.e. adsorb less well to the stationary phase, will move through the chromatography set up faster because there are fewer interactions with the stationary phase to slow the component down. These components will be observed first at the endpoint. Components that adsorb more strongly to the stationary phase have more interactions with the stationary phase to slow down the movement of the component. These components will be observed last at the end point.
2 main types of chromatography to be aware of:
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THIN LAYER CHROMATOGRAPHY
Mobile phase = a solution e.g. ethanol
Stationary phase = TLC plate (silica/alumina)
Components are identified according to their Rf values -
GAS CHROMATOGRAPHY
Mobile phase = inert gas e.g. nitrogent
Stationary phase = chromatography column
Components are identified according to their retention times
Can be combined with mass spectrometry to provide a powerful analysis technique.
