CHROMATOGRAPHY (ANALISIS CHEMISTRY) - Coursework Example

In thin layer chromatography, a thin, uniform layer of silica or alumina gel was traditionally coated on a piece of glass. The mixture was dissolved in an appropriate solvent and the glass plate was immersed in the liquid. The movement of the individual components of a mixture takes place at different rates and the distance travelled by each component is measured and the data so obtained is used to calculate the Rf value is calculated by dividing the distance travelled by the component with the distance travelled by the solvent.

Rf values are then compared with standard values to identify the suspected component. Fluorescent materials are incorporated into the stationary phase to identify colorless components which are invisible to the naked eye. Such components are visualized using ultra violet light. Separation of components of a mixture depends upon their affinity for the solvent as well as the capability of bonding with the stationary phase which is rich in hydroxyl groups. Van der Waals forces also operate between the components and their affinity or repulsion from the stationary phase and determine the distance moved.

Column chromatography was advancement in the technique where the stationary phase was packed inside a column (glass tube) and the mobile phase with the dissolved investigative mixture poured from the top. The movement occurred under the influence of gravity as well as the attraction of the components in the stationary phase, allowing identification of individual components. HPLC (High Performance Liquid Chromatography/High Pressure Liquid Chromatography) is a modern technique used to separate desirable or investigative chemical compounds from other compounds in a liquid sample.

The investigative compounds are dissolved in an appropriate organic or inorganic solvent known as the mobile phase and the mixture is passed under pressure through specific columns which constitute the stationary phase.