<P> The classical preparative chromatography column is a glass tube with a diameter from 5 mm to 50 mm and a height of 5 cm to 1 m with a tap and some kind of a filter (a glass frit or glass wool plug--to prevent the loss of the stationary phase) at the bottom . Two methods are generally used to prepare a column: the dry method and the wet method . </P> <Dl> <Dd> <Ul> <Li> For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry . </Li> <Li> For the wet method, a slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column . Care must be taken to avoid air bubbles . A solution of the organic material is pipetted on top of the stationary phase . This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent . Eluent is slowly passed through the column to advance the organic material . Often a spherical eluent reservoir or an eluent - filled and stoppered separating funnel is put on top of the column . </Li> </Ul> </Dd> </Dl> <Dd> <Ul> <Li> For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry . </Li> <Li> For the wet method, a slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column . Care must be taken to avoid air bubbles . A solution of the organic material is pipetted on top of the stationary phase . This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent . Eluent is slowly passed through the column to advance the organic material . Often a spherical eluent reservoir or an eluent - filled and stoppered separating funnel is put on top of the column . </Li> </Ul> </Dd> <Ul> <Li> For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry . </Li> <Li> For the wet method, a slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column . Care must be taken to avoid air bubbles . A solution of the organic material is pipetted on top of the stationary phase . This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent . Eluent is slowly passed through the column to advance the organic material . Often a spherical eluent reservoir or an eluent - filled and stoppered separating funnel is put on top of the column . </Li> </Ul>

What is column chromatography and how does it work