Chromatography and Instrumentation

• Invented by a Russian Botanist Mikhail Tswett in 1903

• He used chromatography to separate the colour pigments in plants from one another

• Chromatography is a separation technique in which a mobile phase carrying a mixture moves in contact with a selectively adsorbent stationary phase

In English!!!!!• Chromatography involves two phases1. A Mobile phase which can move2. A stationary phase which cannot move

The mixture (such as ink ) is placed on the stationary phase (such as filter paper) and the mobile phase (such as water) passes over it. Different parts of the mixture will have different adherence (attraction) to the stationary phase and mobile phase, the components of the mixture which have a better affinity with the mobile phase will move more easily with the water than those that have a better affinity with the stationary phase

Uses of Chromatography

• Chromatography was originally used to separate coloured substances but now is used to separate a wide variety of different compounds

• It is also used to estimate how much of a particular component is in a mixture

• For example determining the purity of a drug, separate out all the components of the drug and assess how much of the active compound is present

Types of Chromatography

• Paper Chromatography• Thin Layer Chromatography• Column Chromatography• Gas Chromatography• High Performance Liquid Chromatography

Paper Chromatography

• The stationary phase is chromatography paper• The mobile phase is a solvent such as

methanol or water etc.

Thin Layer Chromatography

• More efficient than paper chromatography as the particles in the stationary phase are smaller

• Stationary phase is a thin layer of aluminium oxide or silica gel spread on a glass plate

• Mobile phase is a solvent • Spot of mixture is placed at the end of the plate and then into the solvent

Thin Layer Chromatography

• It is often used to determine the purity of drugs or in forensics to separate colours from dyes extracted from fabrics found at a crime scene to see if the suspect matches

• In many cases the component being separated may not be coloured and the plates may be sprayed with chemicals or looked at with UV light to make some spots visible

Column Chromatography• Thr staionary phase is placed in

a long tube or column• It is commonly made of a solid

adsorbent material such as a gel• Glass wool is placed at the end

to prevent the stationary phase from flowing out

• The mixture to be separated is dissolved in a solvent and added at the top the different components will adhere at different points to the beads and form bands which can be identified

• By adding more solvent each of the different bands may be dissolved out of the column and collected separately in beakers

• NB another term for solvent is Eluent

• Passing a solvent through the column is known as elution

Gas Chromatography

• Gas chromatography uses a gas as the mobile phase

• The stationary phase is a high boiling point liquid (like a ling chain alkane) spread on solid particles (alumina or silica gel beads) that are packed into a column

• This column is kept in an oven and the sample to be analysed is injected into the hot column using a syringe

• The sample is vaporised and carried through the system by an unreactive carrier gas

• The various components are separated out along the column based on their solubility in the solvent

• As each component leaves the column it passes into a detector that records a signal

• This detector then plots a chart where each component shows up as a peak

Uses of Gas Chromatography

• Measure the level of alcohol in blood or urine samples

• Analyse drug test samples from athletes

High Performance Liquid Chromatography

HPLC

• In this type of chromatography a pump is used to force a liquid through a tightly packed column

• The high temperatures needed in gas chromatography are not necessary so more chemicals can be analysed in this way

• The components are detected by a detector and a chart is produced similar to the method in Gas Chromatography

Other Important Instrumental Techniques in Chemistry

• Infra Red Spectrometry• Ultra Violet Sectrometry

Infra Red Spectrometry

• Infra red spectrometry can be used to identify organic compounds

• Infra red radiation is emitted by lots of objects• Different bonds absorb infra red rays of

different wave lengths Eg, A C=C bond would absorb a different wavelength than an O-H bond

• Thus every organic compound has a unique IR spectrum that can serve as a fingerprint for it

IR Spectrum of Polystyrene

Uses of Infra Red Spectrometry

• Identify plastics, illegal drugs etc.

Ultra Violet Spectrometry

• UV spectrometry is used to detect the presence of certain functional groups in molecules

• It may also be used to measure the concentrations of certain organic compounds in solution Eg, in clinical drug trials samples of blood may be taken and analysed to see where the drug is in the body and what is happening to it