Practical investigations
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What is the main advantage of 2-dimensional paper chromatography over a 1-dimensional one?
What are the considerations in choosing a chromatographic solvent?
Corrie writes.......
Sometimes in chromatography two substances will have the same Rf value (travel the same distance) in a particular solvent. Only one spot will be seen although two substances are present.
If the chromatogram is then turned through 90o and eluted with a different solvent, in which the two substances have different Rf values, then two separate spots will develop, enabling identifcation of the two substances.
The substances in the mixture should have different solubilities in the solvent. If they are all very soluble, then they will all move with the solvent front and have high Rf values. On the other hand if they are all insoluble in the solvent then they will not move from the starting point. By considering how polar the substances in the mixture are likely to be, a sensible choice of solvent can be made for preliminary investigation. Then mixtures of solvents of different polarity could be used to achieve better separation.
Risk assessment
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updated: 29 November 2007
