I love hearing about/testing unusual laboratory techniques. Just because you or your colleagues have always done something a certain way, doesn’t mean there isn’t a faster, more effective, or cheaper process available. You also never know when all conventional methods to achieve something will fail (typically when attempting to purify some badass new compound), and you need to dig a little deeper into the tool box… So in case you didn’t hear about this one yet, here I’m highlighting radial chromatography (also known as centrifugal chromatography or centrifugal thin layer chromatography).
Many readers will be all too familiar with column chromatography, frequently used in synthetic chemistry to separate and purify materials. Here, solvent (the mobile phase) is eluted through silica or alumina (the stationary phase) using gravity or applied pressure (see also flash chromatography). You add your crude product mixture on top of the stationary phase, and the various components elute through the column at different speeds. The separated (hopefully now pure!) materials are then collected as they elute out the bottom.
In radial chromatography, solvent is instead eluted using centrifugal force. A circular plate containing a thin layer of silica/alumina is spun at high RPM, with crude material and solvent added in the centre. Continued rotation and addition of solvent separates out the individual components into rings. Eventually these reach the edge of the plate whereby the solution flys off into a specially designed enclosure, runs down the sides, and is collected as per the conventional approach. Using coloured compounds the process is actually rather pretty, as shown in the video below (check it out at ∼2 min).
There are at least two commercially available models (the Chromatotron and the Cyclograph), and apparently they can be made on the cheap from repurposed unused equipment. A fairly recent study in J. Chem. Educ. reports the use of a Chromatotron in undergraduate experiments for the separation of nitroaniline isomers.
Sadly I have never worked in a lab that had one, and only heard of the technique from reading a 2001 Lanny Liebeskind paper. If anyone has ever used these in their research I’d love to know – how do they compare to conventional column chromatography? Can they compete in any way with modern automated flash chromatography systems, such as those offered by Biotage or ISCO?