Chromatography

Chromatography is the process whereby a mixture of chemicals in gas or liquid form (the moving phase) moves over the surface of another matter in liquid or solid form (the stationary phase). Some of the molecules of the moving phase are sucked towards the surface of the solid and stuck there temporarily. As this separation occurs, the components can be easily identified individually since they all move in different ways and at different speeds. There are a wide range of chromatography techniques. One uses paper as the stationary phase, which is dipped in a solvent. Through capillary action, the solvent travels up the paper and separates. In column chromatography, the stationary phase is a vertical glass jar, which is packed with a solid. The moving phase is pumped in at high pressure and splits into components, which are removed for analysis. Also known as vapour-phase (VPC) or gas-liquid partition (GLPC) chromatography, this technique uses gases as the moving phase. A tiny sample is placed in a syringe and injected in the machine where it is vaporised exiting through an electronic detector. Chromatography works with tiny samples and low concentrations and is widely used for forensic science, environmental studies and in medical research.