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

2. PRACTICAL ASPECTS /CONSIDERATIONS ► Columns ► Open column chromatography is commonly carried out with simple glass columns. The dimensions of the columns depend on the quality of material to be separated. The smallest columns are only few millimeters in diameter and of correspondingly greater length.

3. PRACTICAL ASPECTS /CONSIDERATIONS ► Some model experiments are described in chapter 9 where the column sizes are specified. The lower end of the column is drawn out so that it can be connected to stopcock. Or a piece of flexible tubing which can be pinched with screw – clip. ► The adsorbent can be supported on a plug of glass wool or on a porous plate which rests on lugs. The latter is preferable if it is desired to remove the column packing after separation.

4. PRACTICAL ASPECTS /CONSIDERATIONS ► Packing ► In order to obtain maximum efficiency the column must be evenly packed. The influence of particles size and regularity of packing ob column performance has been discussed elsewhere. While open – tubular chromatography using gravity feed solvent is restricted to packing particles >150 µ m ( in order to obtain acceptable flow rates). The column must be packed as uniformly as possible to minimize distortion of the chromatographic boundaries.

5. PRACTICAL ASPECTS /CONSIDERATIONS ► Channeling is usually caused by the inclusion of air bubbles during packing. ► To prevent these effects, so far as possible, the packing material should be slurried with the solvent and poured as a thin stream into the tube, which should be about one third full of the solvent.

6. PRACTICAL ASPECTS /CONSIDERATIONS ► If the adsorbent is allowed to settle gradually – which can be arranged by maintaining gentle agitation while there is solvent flow through the column – reasonably homogenous packing will result. If the particle size of the adsorbent is uniform, it is easier to get homogeneous packing. On no account should any part of the column be allowed to run dry, during packing or during a separation.