What is paper chromatography?
A technique used to identify mixtures in solution
Why does chromatography work?
Because some compounds in a mixture will dissolve better than others in the solvent chosen
How is paper chromatography carried out?
- a capillary tube is used to dab a spot of the solution on a pencil line near the bottom of a sheet of absorbent chromatography paper
- the paper is then placed in a solvent at the bottom of a beaker or tank
- the solvent is allowed to soak up the paper, running past the spot of mixture
What determines how far the components in a mixture travel up the paper?
Their relative solubility (the more soluble a substance is in the solvent, the further up the paper it is carried)
How can the compounds in a mixture be identified through chromatography?
Their chromatogram can be compared with others obtained from known substances
What is needed to compare chromatograms?
The same solvent at the same temperature as used to generate the data held in a database or book of data must have been used
How is the data for chromatograms presented?
As an Rf (retention factor) value
What is the retention factor (Rf)?
This is a ratio, calculated by dividing the distance a spot travels up the paper by the distance the solvent front travels
What are instrumental techniques used for?
Fighting pollution and healthcare
What are the benefits of modern instrumental methods over older methods?
- highly accurate and sensitive
- quicker
- enable very small samples to be analyzed
What are the detriments of modern instrumental methods over older methods?
- usually very expensive
- takes special training to use
- gives results that can often be interpreted only by comparison with data from known substances
