Paper chromatography

The types of the paper chromatography

PAPER CHROMATOGRAPHY, the chromatography on the paper (EN: paper chromatography; DE: Papierchromatographie; FR: Chromatographie sur papier; ES: cromatografia sobre papel; RU: бумажная хроматография) is the method for the separation and analysis of the mixtures of the substances, which is based on their distribution between the mobile and immobile liquid phases; they are using paper as the carrier for the immobile liquid phase. The method has been proposed by the British scientists Archer Martin and Richard Synge during the 1941.

They use for the paper chromatography the special grades of paper, which are differing by the numbers, with the increasing of which the density of the paper increases. The paper holds the water within the pores, which is the immobile liquid phase. They place the solution of the sample in the form of droplets onto the sheet of paper at the certain distance from the edge. After the evaporation of the solvent, they place the edge of the sheet into the hermetic chamber, which is containing the developer substance, namely, the movable liquid phase (for example, alcohols, ketones, phenols, carbon tetrachloride, chloroform, and other mixtures of these substances, and also the mixtures with inorganic solvents). During this process, there proceeds the movement of the original spot along the current of the developer substance, and the separation of the mixture into the components. If the substances are not coloured, then they develop the chromatogram, for example, using the spraying with the solution of the indicator, view the chromatogram under the ultraviolet rays, and so on. The ratio of the distance Rf, which has been traveled by the spot I, to the distance, which has been traveled by the front of the developer substance m, under the identical conditions of the experiment, is the constant value; the Rf ratios differ in terms of value for different substances, and may be used for the identification of the compounds. The quantitative determinations of various substances within the spots of the chromatogram are conducted by the usual analytical methods. They distinguish the one-dimensional, two-dimensional, circular, columnar, and electrophoretic chromatograms (the Figure).

Using the method, which is described above, they register the one-dimensional chromatograms. They obtain the two-dimensional chromatogram, using the separation of the spots from the one-dimensional chromatogram by another developer substance, in the direction, which is perpendicular to the first row of the spots. On the circular chromatogram, they wash the spot, which is placed into the centre of the sheet, along the concentric circles. In case of the columnar paper chromatography, they conduct the separation on the paper discs, which are tightly inserted into the cylindrical column. For the obtainment of the electrophoretic chromatograms, they impregnate the paper sheet with the electrolyte, fixate the sheet between the electrodes, apply the mixture, which should be analyzed, connect the electrodes to the source of the direct electric current, and simultaneously deliver onto the paper the movable solvent along the direction, which is perpendicular to the lines of force of the electric current. In case of this method, the separation of the components proceeds as the consequence of their unequal distribution between the two liquid phases, and of the different velocity of the movement of the substances under the influence of the electric field.

They use the paper chromatography for the separation and analysis of the inorganic and organic substances within the natural and industrial materials (for example, they determine the tars within the petroleum products, the rare-earth elements within the rocks and minerals).