Flash column chromatography is a routine method for separating mixtures into their constituent compounds on a small scale where alternative methods for separation (e.g. recrystallisation or distillation) are impractical or difficult to carry out.

A flash column consists of a stationary phase (for ‘normal phase’ chromatography this is usually a polar silica gel) that is held in a glass column fitted with a tap at the base and a ground-glass joint at the top. The sample is loaded to the top of the stationary phase and the mobile phase (or solvent) is passed through the silica at an increased pressure (using bellows or compressed air). The mobile phase carries the sample through the column with the different components separating as they progress through the column due to their differing retentions. The solvent is collected in fractions from the tap and can be analysed by TLC to identify which products are present in each sample. Flash column chromatography was initially reported by W Clarke Still et al. in 1978.¹

¹W Clarke Still, M Kahn, A Mitra J. Org. Chem., 1978, 43, 2923.

Stationary phases

A wide range of stationary phases are used for column chromatography, including polar ('normal phase') and non-polar ('reversed phased') packing materials. The most common stationary phase used in teaching labs is silica: