A sample that requires analysis is often a mixture of many components in a complex matrix. For samples containing unknown compounds, the components must be separated from each other so that each individual component can be identified by other analytical methods. The separation properties of the components in a mixture are constant under constant conditions, and therefore once determined they can be used to identify and quantify each of the components. Such procedures are typical in chromatographic and electrophoretic analytical separations.
A mixture can be separated using the the differences in physical or chemical properties of the individual components. As an example, dumping spaghetti and water in a colander separates the two components because the liquid water can run through the colander but the solid spaghetti cannot (assuming that it is not grossly overcooked as prepared in some university dining halls). Some water will stick to the spaghetti and some spaghetti may go down the drain because the colander is not 100% efficient. An analagous example is the filtering of a solid precipitate to separate it from a solution. These separations are based on the states of matter of the two components, other physical properties that are useful for separations are density and size. Some useful chemical properties by which compounds can be separated are solubility, boiling point, and vapor pressure.