Flash Chromatography

  Because the elution rate of the mobile phase in regular column chromatography as described above is controlled primarily by gravity, chromatographic runs can potentially take a very long time to complete. Flash chromatography is a modified method of column chromatography in which the mobile phase moves faster through the column with the help of either pressurized air or a vacuum. A vacuum line is attached to the bottom of the separating column, this pulls the mobile phase solvent, and the components in the mobile phase, through the column at a faster rate than gravity does. A figure of this set-up can be seen in the links section. Flash chromatography is powered by compressed air or air pumps works by pushing the mobile phase through the column and achieves faster flow rates of the mobile phase just as vacuum facilitated flash chromatography does. For this method, a pressurized air line is attached to the top of the separating column. It is for this reason that flash chromatography is also referred to as medium pressure chromatography. An inert gas is used as to not interact with the mobile or stationary phase or the component mixture. Nitrogen gas is commonly used for this method of chromatography. Many instruments are available to perform flash chromatography as efficiently as possible: expensive columns, pumps, and flow controllers. This maintains a constant and precise air pressure or vacuum to the column in order to obtain steady flow rate of the mobile phase and favorable separation of the samples in solution. However, less expensive alternatives are available, as flow controllers can be made so that pressurized air can be used to facilitate flash chromatography.

By using the above apparatus, purchasing expensive air pumps can be avoided. This method is useful to an extent. Since the flow rate of the pressurized gas is controlled manually by the flow rate controller, it is more difficult to quantify the flow rate and keep that flow rate constant. Instruments available for flash chromatography are able to set flow rates digitally and keep flow rate constant.

Flash chromatography is similar to HPLC in that the mobile phase is moved through the column by applying pressure to the solvent in order to achieve a quicker result. However, in flash chromatography, only medium pressure is applied to the system within the solution. In HPLC, pressures as high as 5000 psi can be applied in the column by high performance pumps.