Chromatography Techniques Chemistry Tutorial

Key Concepts

• Chromatography is an analytical technique used to determine the purity of a substance or to separate a mixture into its components.
• The stationary phase refers to the solid or liquid to which components in a mixture bind or adsorb.
• The mobile phase refers to the liquid or gas that moves the components in a mixture over the stationary phase.
• Components in a mixture are separated based on their different abilities to bind or adsorb to the stationary phase, and on their different abilities to desorb or dissolve in the mobile phase.
• In paper chromatography and thin layer chromatography the retardation factor, R_f, is a comparison of the distance travelled by a component to the distance travelled by the solvent.
• In gas chromatography and high-performance liquid chromatography, the time retained in the column, the retention time (R_t), is measured.

Please do not block ads on this website.
No ads = no money for us = no free stuff for you!

Comparison of Chromatography Techniques

Type	Features	Uses
Paper	inexpensive slow often used for water soluble compounds a qualitative technique stationary phase: usually water (present in the paper); mobile phase:pure solvent or solvent mixture Retardation factor, Rf, measured	identification of colours in inks or foods identification of amino acids separation of pigments in plant leaves
Thin Layer (TLC)	inexpensive faster than paper and more sensitive used for less polar compounds qualitative technique although components may be scraped off the plate & their masses measured stationary phase: plate coated with silica gel or Al2O3; mobile phase:pure solvent or solvent mixture Retardation factor, Rf, measured	identification of biological sugars identifying components of pain-relieving preparations identifying components (eg, carboxylic acids) that might damage paper
Gas (GC, GLC)	area under the peak measures the amount of the component present
	expensive fast used for gases or easily vaporised compounds relative molecular mass (Mr) < 300 both qualitative and quantitative technique stationary phase: a liquid adsorbed onto an inert solid; mobile phase (carrier gas): an inert gas such as helium, nitrogen Retention time, Rt, measured	analysis of air-borne pollutants analysis of athletes' urine samples for performance enhancing drugs analysis of oil spills analysis of essential oils in perfume preparation
High-performance Liquid (HPLC)	area under the peak measures the amount of the component present
	expensive but less expensive than gas chromatography (GC) fast but slower than gas chromatography (GC) used for organic compounds that decompose if vaporised or compounds with relative molecular mass (Mr) > 300 both a qualitative and a quantitative technique stationary phase: small waxy solids; mobile phase (eluent): pure solvent or solvent mixture Retention time, Rt, measured	analysis of pharmaceuticals cyanide analysis analysis of organic pollutants in water analysis of toxic compounds in shell fish protein analysis