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.
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.
Similarly, an atmospheric humidity of 100% represents the saturation point, at which the air can hold no more moisture.
For magnetic materials, saturation is the state when the material cannot absorb a stronger magnetic field, such that an increase in magnetization does not produce significant change in magnetic flux density.
Note: Modulation often requires that amplifiers operate below saturation.