To separate mixtures containing substances of widely differing polarities, a technique called “flip-flop chromatography” has been introduced. The sample is deposited in the pores of a solid ( e.g., silica) with an average pore diameter of about 100 » to increase its surface area and hence its rate of extraction. Depending on the pore volume of the silica, up to 40 % (w/w) of sample may be loaded. The essence of flip-flop chromatography is that the sample column is extracted by a combination of four or more polar and non-polar solvents which are applied in order of alternating polarity beginning with the most extreme so that the tail ends of the polarity distribution of the sample are successively extracted, leaving behind material with a more restricted polarity range, increasing the selectivity of later extractions. All the polar solvents are washed through the sample column in one direction and the non-polar eluents in the opposite direction. The sequence of solvents cn be 1, water; 2, heptane; 3, methanol; and 4, methylene chloride. At either end of the sample column stripping columns (packed with silica or a reversed phase) prevent the removal of substances whose polarity is very different from that of the solvent. The mechanism of the separation is a combination of extaction, frontal analysis and displacement chromatography, but definitely not the conventional adsorption chromatography. However, the influence of the support on the separation is not negligible. The advantages of flip-flop chromatography are: (1) improved quality of sepation compared to conventional extraction, (2) high speed of separation, (3) economy in the use of solvents, (4) high sample concentrations (up to 5%) in the fractions, (5) the simplicity of the apparatus. As an illustration of this method, the heart flycoside uscharine, was recovered from freeze-dried Calotropis gigantea sap. Both the yield and the degree of purification achieved are better with this method than with stepwise extraction.