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Chromatography is defined as “the separation of a mixture by passing it in solution or suspension or as a vapor (as in gas chromatography) through a medium in which the components move at different rates.”
Chromatography essentially is a technique for separating the components (solutes) of a mixture and determining the relative amounts of each solute distributed between a moving fluid stream, called the mobile phase, and a contiguous stationary phase. The mobile phase may be either a gas or a liquid, while the stationary phase is either a liquid or a solid.
Chromatography is one of several separation techniques defined as differential migration from a narrow initial zone. Electrophoresis is another member of this group. In this case, the driving force is an electric field, which exerts different forces on solutes of different ionic charge. The resistive force is the viscosity of the nonflowing solvent. The combination of these forces yields ion mobilities peculiar to each solute.
Chromatography has numerous applications in biological and chemical fields. It is widely used in biochemical research for the separation and identification of chemical compounds of biological origin. In the petroleum industry the technique is employed to analyze complex mixtures of hydrocarbons. Other industries that use chromatography can include environmental (ie., pesticide analysis), forensic science, food and beverage, and manufacturing.
Chromatography is a common name for techniques based on the partition of the molecules to be analyzed between a mobile and a stationary phase. Separation is the result of different partitions of molecules between the two phases. Because the best separation of any solutes can be obtained under equilibrium conditions, analytical chemists prefer to use chromatographic systems that are as near to the equilibium state as possible.
However, in the case of preparative chromatography, where the main objective is not the optimal separation of solutes but the maximum yield of one or more solutes at a given purity, the situations entirely different. Preparation chromatographic separations are generally not equilibrium processes. The high sensitivity, selectivity, and reproducibility of chromatographic methods have been extensively exploited in food and nutrition science and technology. This chapter overviews the theoretical backgrounds, principles, and fundamental technical characteristics of chromatographic separation processes and instrumentations.