There are many instances when it is necessary to remove traces of water from a solution or liquid. One common example is the drying of an organic layer after a solvent extraction. The technique involves adding a suitable solid drying agent to the liquid followed by its removal by gravity filtration.

Drying agents should be insoluble in the solvent to be dried as well as unreactive toward both the solvent and the solute. Drying agents should also remove water quickly and be easily removed by filtration.

Drying Agent



The most commonly used drying agent with high efficiency and low reactivity.


Has the capacity to remove a great deal of water but slowly. It will also react with compounds containing O and N groups. This drying agent is best reserved for use in guard tubes.


Not as efficient as MgSO4 but can be used in certain situations.


A fast and efficient drying agent but with a lower capacity for water than MgSO4


Quite a good drying agent but restricted for use with non-acidic solutions.

Molecular sieves

A very efficient drying agent that must be ‘activated’ in a hot oven and then allowed to cool before use.