Column Chromatography - Automated Systems

Automated Systems

Column chromatography is an extremely time consuming stage in any lab and can quickly become the bottleneck for any process lab. Therefore, several manufacturers like Teledyne Isco, have developed automated flash chromatography systems (typically referred to as LPLC, low pressure liquid chromatography, around 350-525 kPa (50-75 psi)) that minimize human involvement in the purification process. Automated systems will include components normally found on more expensive high performance liquid chromatography (HPLC) systems such as a gradient pump, sample injection ports, a UV detector and a fraction collector to collect the eluent. Typically these automated systems can separate samples from a few milligrams up to an industrial kg scale and offer a much cheaper and quicker solution to doing multiple injections on prep-HPLC systems.

The resolution (or the ability to separate a mixture) on an LPLC system will always be lower compared to HPLC, as the packing material in an HPLC column can be much smaller, typically only 5 micrometre thus increasing stationary phase surface area, increasing surface interactions and giving better separation. However, the use of this small packing media causes the high back pressure and is why it is termed high pressure liquid chromatography. The LPLC columns are typically packed with silica of around 50 micrometres, thus reducing back pressure and resolution, but it also removes the need for expensive high pressure pumps. Manufacturers are now starting to move into higher pressure flash chromatography systems and have termed these as medium pressure liquid chromatography (MPLC) systems which operate above 1000 kPa (150 psi).

The software controlling an automated system will coordinate the components, allow a user to only collect the fractions that contain their target compound (assuming they are detectable on the system's detector) and help the user to find the resulting purified material within the fraction collector. The software will also save the resulting chromatograph from the process for archival and/or later recall purposes.

A representative example of column chromatography as part of an undergraduate laboratory exercise is the separation of three components (out of 28) in the oil of spearmint: carvone, limonene and dehydrocarveol. A microscale setup consisting of a Pasteur pipette as column with silica gel stationary phase can suffice. The starting eluent is hexane and solvent polarity is increased during the process by adding ethyl acetate.