In the Dark

When working on solutions and separating molecules into fractions (groups of molecules) we want to try and ensure that none of the molecules break down and become something else.  For example, some molecules are light sensitive and can break down in the presence of too much light.  For this reason we try and keep solutions, and columns with molecules loaded onto them, in the dark when we are not working on them.

Solutions in small conical flasks, or dried down fractions in vials, are kept in a fridge.  Not only is it dark in the fridge (yes the light does go off when you shut the door), but it is also cold.  As you know, reactions happen at a much slower rate at low temperatures, so any potential reactions that could occur will hopefully be slowed right down.

Larger conical flasks containing solutions are kept in a dark cupboard.

Sometimes when large volumes of solution are being passed through a column, the column is left to run for quite a long period of time.  To keep light out the whole apparatus is wrapped in tinfoil.