A widely used chromatographic technique for separating the components of mixtures using absorbent paper as the stationary phase. A sheet or strip of paper, with a concentrated spot of the mixture on a pencil-drawn base line, is vertically suspended in a suitable solvent (the mobile phase), that seeps slowly upwards through the paper by capillary action. The compounds in the mixture travel upwards with the solvent and separate out at different levels. When the solvent reaches a level near the top of the paper, this point (the solvent front) is marked. The paper is removed and dried. Colourless compounds may then be developed either by spraying the paper (the chromatogram) with a suitable chemical, such as ninhydrin, or by viewing the paper in ultraviolet light. The compounds can then be identified either by comparing them with chromatograms of known standard solutions run at the same time, or by calculating the * Rf values. See partition chromatography , two-dimensional analysis. |
