In chemistry, saturation has three meanings:

1. In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance. This point, the saturation point, depends on the temperature of the liquid as well as the chemical nature of the substances involved. This can be used in the process of recrystallisation to purify a chemical: it is dissolved to the point of saturation in hot solvent, then as the solvent cools and the solubility decreases, excess solute precipitates. Impurities, being present in much lower concentration, do not saturate the solvent and so remain dissolved in the liquid. If a change in conditions (e.g. cooling) mean that the concentration is actually higher than the saturation point, the solution has become supersaturated.
2. In organic chemistry, saturation refers to an organic compound having the maximum amount of hydrogens possible: i.e., no double bonds or when every carbon atom in a hydrocarbon chain is attached to two hydrogen atoms. Of simple hydrocarbons, alkanes are saturated, and alkenes are unsaturated. In the modern treatment of electronic structure, unsaturated compounds are characterized by pi electron systems. The term is applied similarly to the fatty acid constituents of lipids, where the fat is described as saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. Unsaturated is used when any carbon structure containing double or occasionally triple bonds. Many vegetable oils contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them.
3. In biochemistry the term saturation refers to the fraction of total protein binding sites that are occupied at any given time.

See also

• Saturated fat
• Unsaturated fat