Author(s): Georges Guiochon, L A Beaver, M F Gonnord, Maheran Zakaria
Two-dimensional column chromatography is a method which combines the advantages of column chromatography (constant, adjustable flow velocity, excellent efficiency, on-line detection) and two-dimensional thin-layer chromatography (successive developments in two perpendicular directions, using two different retention mechanisms). It is shown that by merely keeping constant the solvent flow velocity during the development of a thin-layer plate, a considerable increase in the spot capacity can be achieved, since plate length and particle size can be selected without any prejudicial influence on the solvent velocity which can be kept constant at the value considered as optimum by the analyst. Calculations show that two-dimensional column chromatography can generate peak capacities well in excess of 500, up to several thousands, and that the specifications for the equipment are not too stringent. A 10 × 10 cm column would be 1 mm thick, be well packed with 10-μm particles and be operated at a reduced velocity of 10. Such a packing could be expected to be very homogeneous (A = 0.7) and the reduced plate height would be 1.95. The expected spot capacity is 900, while the pressure drop for a compound with a diffusion constant D = 5 × 10-6, cm2/sec (linear velocity, u, = 0.05 cm/sec) and a solvent with viscosity 1 cP is only 5 atm (flow-rate 3 cm3/min). The sample spot should be about 1 mm in diameter or less. Equipment capable of these performances is under construction. Successful operation of this two-dimensional separation scheme, however, relies on the ability to find two chromatographic systems operating according to widely different mechanisms.