How do you select solvents for chromatography?

Solvents for chromatography are selected based on their polarity and the nature of the compounds to be separated.

In chromatography, the choice of solvent, also known as the mobile phase, is crucial as it directly influences the separation of components in a mixture. The main factor to consider when selecting a solvent is its polarity, which should match the polarity of the compounds to be separated. This is because like dissolves like; polar compounds will dissolve in polar solvents and non-polar compounds in non-polar solvents.

For instance, if you are trying to separate a mixture of polar compounds, you would choose a polar solvent such as water or methanol. On the other hand, if you are dealing with non-polar compounds, a non-polar solvent like hexane would be more suitable. Sometimes, a mixture of solvents may be used to achieve the desired polarity.

Another factor to consider is the solvent's ability to dissolve the sample. The solvent should be able to dissolve a sufficient amount of the sample to allow for effective separation. Additionally, the solvent should not react with the sample or the stationary phase (the material on which the sample is placed).

The boiling point of the solvent is also important. A solvent with a low boiling point is preferred as it will evaporate quickly, speeding up the chromatography process. However, if the solvent's boiling point is too low, it may evaporate before the separation is complete, which would not be ideal.

Lastly, the solvent should be safe to use. It should not be toxic or flammable, and it should be easy to dispose of after use. Safety should always be a priority in any laboratory procedure, including chromatography.

In summary, the selection of solvents in chromatography is a careful balance of several factors, including polarity, solubility, boiling point, and safety.