Thin Layer Chromatography and Gas Chromatography for the Purpose of Separation

We performed several experiments featuring organic synthesis, mechanistic studies, and modern instrumental techniques for the separation and characterization of organic compounds. The experiments I found to be of most interest included those involving thin layer chromatography and gas chromatography for the purpose of separation.

Chromatography is a chemistry technique for separating the components, or solutes, of a mixture on the basis of the relative amounts of each solute distributed between a moving fluid, called the mobile phase, and a contiguous stationary phase. The mobile phase may be either a liquid or a gas, while the stationary phase is either a solid or a liquid. Kinetic molecular motion continuously exchanges solute molecules between the two phases. If, for a particular solute, the distribution favors the moving fluid, the molecules will spend most of their time migrating with the stream and will be transported away from other species whose molecules are retained longer by the stationary phase. For a given species, the ratio of the times spent in the moving and stationary regions is equal to the ratio of its concentrations in these regions, known as the partition coefficient. A mixture of solutes is introduced into the system in a confined region or narrow zone, where the different species are transported at different rates in the direction of fluid flow. The driving force for solute migration is the moving fluid, and the resistive force is the solute affinity for the stationary phase; the combination of these forces, as manipulated by the analyst, produces the separation.

As a separation method, chromatography has a number of advantages over older techniques including crystallization, solvent extraction, and distillation, for example. It is capable of separating all the components of a multicomponent chemical mixture without requiring an extensive foreknowledge of the identity, number, or relative amounts of the substances present. It...