Flash Column Chromatography

Flash chromatography, also known as medium pressure chromatography, developed  by Clark Still of Columbia University in 1978, as an alternative to  gravity column chromatography. Smaller Silica gel and using Air/Nitrogen to push the solvent gradient down the column. Faster separation, lesser amount of solvent, silica are its advantages.

Procedure described in the paper :
1. A solvent /mixture of solvents  is chosen which gives good separation and moves the desired component to Rf = 0.35 on TLC.
2. A column of the appropriate diameter refer Table I in paper is selected and filled with 5-6 inches of dry 40-63 micrometer (250-400 mesh ) silica gel.
3. The column is filled with solvent and pressure is used to rapidly push all the air from the silica gel.
4. The sample is applied and the column is refilled with solvent and eluted at a flow rate of 2 inches per minute.

Reference :  Rapid chromatographic technique for preparative separations with moderate resolution.
Still, C. W;Kahn, M;Mitra, A. J.Org.Chem., 1978, 43(14), 2923.