Chromatography

Chromatography Separation of a mixture based on the strength of intermolecular bonds of the constituents. Applications include: Pharmaceutical research Detection of banned or illegal substances Forensics eg. Identification of explosives Many, many more

Key Terms Mobile phase Stationary phase Adsorption Desorption Rf value Solute Solvent Solvent front Origin

Paper Chromatography Stationary phase is paper. Mobile phase is a liquid, commonly water, but could be ethanol or a non-polar solvent.

Thin Layer Chromatography Similar to paper chromatography but quicker and more precise. A layer of material (eg. Silica gel, aluminium oxide) is coated onto glass or aluminium. This serves as the stationary phase.

Rf Values Retention factor. A measure of a substance’s affinity for the stationary phase. Rf = distance moved by solute distance moved by solvent

Instrumental Chromatography Much more commonly used in laboratories these days. Quicker More accurate Less room for human error Sensitive Can be non-destructive

Gas Chromatography (GC) Mobile phase – inert gas such as helium or nitrogen. Stationary phase – column containing a liquid and coated in inert granules.

Gas Chromatography (GC) Put these steps in the correct order. Components of sample are detected by a suitable detector. Sample is placed in injection port where it is heated. Sample passes through the column which separates the components. Evaporated sample is carried through a tube by an inert gas. Based on this description, what kind of substances would NOT be suitable for analysis with GC?

Gas Chromatograms The position of the peak is the Rf value of each component. The area under the peak represents the amount of each component present.

Gas Chromatograms Which peaks represent the following substances? Which is the most abundant substance present? Methanol Ethanol Butanol Propanol Hexane

Standards Included in the mixture to give a reference point for Rf values. A known concentration of a substances is included and compared to the results for the analyte.

Detectors Flame ionisation Atomic emission Infrared Mass spectometer Sample burned in hydrogen, forms cations which cause potential difference between two electrodes. Atomic emission Sample burned, elements then heated to the point that they emit specific wavelengths of light. Infrared Mass spectometer

High Performance Liquid Chromatography (HPLC) Used for analysing liquids with high boiling points. Stationary phase – Short fractioning column. Mobile phase – Solvent selected based on polarity.

Image Credits ‘Paper chromatography’ By Ewan (Own work) (http://commons.wikimedia.org/wiki/File:Chromatography_tank.png#file) via Wikimedia Commons ‘Effects of changing solvent’ By Rhannosh (Own work) (http://upload.wikimedia.org/wikipedia/commons/8/88/Changing_Solvents_TLC.png), via Wikimedia Commons ‘HPLC Apparatus’ By WYassineMrabetTalk, This vector image was created with Inkscape (http://upload.wikimedia.org/wikipedia/commons/a/a0/HPLC_apparatus.svg), via Wikimedia Commons