Chromatography

Chromatography techniques

Chromatography separates mixtures using a stationary phase and a mobile phase. Components that interact more strongly with the stationary phase move more slowly. TLC: silica/alumina on a plate (stationary), solvent (mobile); adsorption; $R_f=\frac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$; colourless spots shown by UV, iodine or ninhydrin (amino acids). Gas chromatography (GC): liquid coating on a column (stationary), inert carrier gas (mobile); separation by partition and boiling point; retention time identifies compounds; peak area gives relative amount. GC–MS feeds each separated component into a mass spectrometer for identification. Column chromatography and HPLC separate larger quantities.