Chromatograph

Chromatography is a laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase. The various constituents of the mixture travel at different speeds, causing them to separate. The separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation.

Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for more advanced use (and is thus a form of purification). Analytical chromatography is done normally with smaller amounts of material and is for measuring the relative proportions of analytes in a mixture. The two are not mutually exclusive.

Types of Chromatography

Chromatography techniques can be classified based on the mechanism of separation. The most common types include:

• Gas Chromatography (GC): Separates analytes vaporized without decomposition. A gas stream (mobile phase) carries the compounds through a column containing a stationary phase.
• High-Performance Liquid Chromatography (HPLC): Utilizes high pressure to push solvents containing the sample mixture through a column filled with a solid adsorbent material.
• Thin Layer Chromatography (TLC): Involves samples being deposited on a glass, plastic, or aluminum foil, which is coated with a thin layer of adsorbent material. The plate is then dipped in a solvent that moves up the plate via capillary action.
• Ion Exchange Chromatography: Separates ions and polar molecules based on their affinity to the ion exchanger. It can be used for almost any kind of charged molecule including large proteins, small nucleotides, and amino acids.
• Size Exclusion Chromatography (SEC): Also known as gel permeation chromatography, it separates molecules based on their size.
• Affinity Chromatography: Is highly selective, separating compounds based on a specific interaction between an analyte molecule and a molecule that is immobilized on a stationary phase.

Applications

Chromatography is used in both qualitative and quantitative analysis of both organic and inorganic samples. It has a wide range of applications:

• In the pharmaceutical industry, it is used for purifying raw materials, checking product purity, and quality control.
• In environmental monitoring, it helps in detecting pollutants in air, water, and soil.
• In research, it is used for separating compounds in the synthesis of new chemicals, or in the analysis of biological samples.
• In the food industry, it is used for analyzing food products to ensure quality and to check for contaminants.

History

The concept of chromatography was first introduced by Mikhail Tswett in 1903. He used the technique for the separation of plant pigments such as chlorophyll, which he separated into a series of colored bands on a column of calcium carbonate. Since then, the method has evolved significantly, incorporating new types and techniques for a wide range of analytical applications.

See Also

• Analytical Chemistry
• Biochemistry
• Separation Processes