Chromatography
Chromatography is a method of separating a substance into its components through a physical separation method that involves a stationary phase and a mobile phase. Typically the molecules of a solute are drawn to either the stationary phase or the mobile phase more strongly, and this results in a separation.
and Retention Time
, or the retardation factor, is the fraction of a sample in a mobile phase. With regards to paper chromatography and TLC, it is calculated as:
The retention time refers to the time spent by a compound in the column in GC or HPLC.
Both uniquely identify a compound under the same conditions.
TLC
TLC stands for Thin Layer Chromatography. A thin stationary phase (such as a piece of paper) is dipped in a mobile phase, a liquid solvent. A line is drawn in pencil on the stationary phase above the mobile phase, and a substance placed on the line. The mobile phase progresses up the stationary phase, causing the components of the substance to be separated based on their attraction to the stationary phase compared to their attraction to the mobile phase.
GC
GC stands for Gas Chromatography. A vaporised substance (to be analysed) is injected into a column along with a carrier gas, the mobile phase, usually an inert or unreactive gas. The stationary phase is a layer of liquid or polymer inside a piece of tubing. The compounds within the substance interact with the walls of the tubing (named a column), which is coated with the stationary phase. Each compound progresses based on their attraction to the stationary phase as opposed to the mobile phase, and this causes them to leave the column ('elute') at different times.
HPLC
HPLC stands for High-Performance Liquid Chromatography. HPLC uses pumps to pass a pressurised liquid solvent (the mobile phase) through the substance to be analysed through a column containing the stationary phase. The sample's constituent compounds interact differently with the stationary phase, causing a separation of the compounds.