1. Chromatography Dr.Tawfeq A. Al-Howiriny Associate Professor talhowiriny@yahoo.com

2. Elution Development ► Elution development is the technique most widely used in the various methods chromatography (GC, GLC, LLC and LSC). ► A small sample mixture is introduced on the column and is eluted wit a mobile phase which has a lesser affinity for the stationary phase than the sample components. The components therefore move a long at a rate determined by their relative affinity for the stationary phase but at a lower rate than the eluent. The components are eluted in order of their affinities but their migration is determined by the ternary interaction between components, stationary phase and mobile phase, since the components can be completely separated with a zone of mobile phase between them, elution chromatography is used for analytical separation with some variation possible.

3. Elution Development ► In simple elution chromatography the column is eluted with the same solvents all the time. This is the most suitable when components have similar affinities for the stationary phase and are therefore eluted rapidly, one after another. ► Stepwise elution is carried out by changing the eluent after the predetermined period of time. The eluents are chosen to have increasing eluting power that is, increasing affinity of the mobile phase for the components remaining on the column, and therefore "releasing" them from the stationary phase, enabling them to move through the system.

4. Elution Development ► Gradient elution uses a gradual change in composition of the eluting solvents to achieve separation of components of widely varying affinities for the stationary phase. The ratio of two or more solvents is gradually changed to increase slowly the eluting power of the mobile phase.

5. THEORETICAL CONSIDERATION THEORETICAL CONSIDERATION ► Chromatography is a dynamic separation system consisting of two media, a stationary phase and a mobile phase. The stationary phase consists of small solid particles (usually less than 150 µ m in diameter) with a microporous surface, which may packed into a column or coated on to a plate. These particles are sometimes coated with an inert chemical agent to modify the surface properties

6. THEORETICAL CONSIDERATION THEORETICAL CONSIDERATION ► The mobile phase may be a gas or a liquid and serves to carry the sample component molecule through the chromatic system. During this procedure the component or solute molecules in the mobile phase come into contact with the stationary phase. There is now competition between the two phases for the solute molecules which depends on their physical properties and affinity for the stationary phase. This process is termed partition with each component (A, B,C etc) distributed between the stationary phase (s) and mobile phase (m) as they pass through the system.