Column Chromatography

The stationary phase in column chromatography is most typically a fine adsorbent solid; a solid that is able hold onto gas or liquid particles on its outer surface. The column typically used in column chromatography looks similar to a Pasteur pipette (Pasteur pipettes are used as columns in small scale column chromatography). The narrow exit of the column is first plugged with glass wool or a porous plate in order to support the column packing material and keep it from escaping the tube. Then the adsorbent solid (usually silica) is tightly packed into the glass tube to make the separating column. The packing of the stationary phase into the glass column must be done carefully to create a uniform distribution of material. A uniform distribution of adsorbent is important to minimize the presence of air bubbles and/or channels within the column. To finish preparing the column, the solvent to be used as the mobile phase is passed through the dry column. Then the column is said to be "wetted" and the column must remain wet throughout the entire experiment. Once the column is correctly prepared, the sample to be separated is placed at the top of the wet column. A photo of a packed separating column can be found in the links.