Chromatography separates and identifies the components of a mixture. Every type has two phases:The stationary phase does not move. It is a solid, or a liquid held on a solid support.
The mobile phase moves through or over the stationary phase, carrying the mixture with it. It is a liquid or a gas.The components separate because each has a different relative affinity for the two phases. This can be by adsorption (how strongly a component sticks to the surface of a solid stationary phase) or by relative solubility in a liquid stationary phase compared with the mobile phase. A component that is strongly attracted to the stationary phase spends more time held back and moves slowly. A component with more affinity for the mobile phase is carried along quickly.The three types you need are:Thin-layer chromatography (TLC): stationary phase is a thin layer of silica or alumina on a plate; mobile phase is a liquid solvent. Components are identified by Rf values.
High performance liquid chromatography (HPLC): stationary phase is small solid particles packed in a column; mobile phase is a liquid forced through under high pressure.
Gas chromatography (GC): stationary phase is a liquid on a solid support in a long column; mobile phase is an unreactive carrier gas.In HPLC and GC, components are identified by their retention time, the time taken to pass through the column.Worked example: in TLC on silica, compound X is more strongly adsorbed than compound Y. X moves more slowly, so Y travels further up the plate and has the larger Rf.
The mobile phase moves through or over the stationary phase, carrying the mixture with it. It is a liquid or a gas.The components separate because each has a different relative affinity for the two phases. This can be by adsorption (how strongly a component sticks to the surface of a solid stationary phase) or by relative solubility in a liquid stationary phase compared with the mobile phase. A component that is strongly attracted to the stationary phase spends more time held back and moves slowly. A component with more affinity for the mobile phase is carried along quickly.The three types you need are:Thin-layer chromatography (TLC): stationary phase is a thin layer of silica or alumina on a plate; mobile phase is a liquid solvent. Components are identified by Rf values.
High performance liquid chromatography (HPLC): stationary phase is small solid particles packed in a column; mobile phase is a liquid forced through under high pressure.
Gas chromatography (GC): stationary phase is a liquid on a solid support in a long column; mobile phase is an unreactive carrier gas.In HPLC and GC, components are identified by their retention time, the time taken to pass through the column.Worked example: in TLC on silica, compound X is more strongly adsorbed than compound Y. X moves more slowly, so Y travels further up the plate and has the larger Rf.