A laboratory technique for identification of herbs and their constituents, taking advantage of the different rates at which molecules diffuse through an absorbent column to separate them.
Herbs are composed of alkaloids, saponins, esters, oils etc. In order to trace these in sample plant material, a picture is taken by a process known as Thin-layer-chromatography (TLC) on which a silica- gel coated ‘negative’ makes visible a number of constituents.
To initiate this process, active constituents (alkaloids etc) are extracted and separated. Their separation is possible by dipping into a special solvent solution, after which the ‘negative’ is developed by spraying with a reagent that reveals the constituents in various colours. Each component of the plant has its own distinctive colour. Each herb has its own specific ‘profile’ which can be ‘read’ by the technician and checked against known control samples. Each plant can thus be accurately identified.
n. any of several techniques for separating the components of a mixture by selective absorption. Two such techniques are quite widely used in medicine, for example to separate mixtures of amino acids. In one of these, paper chromatography, a sample of the mixture is placed at the edge of a sheet of filter paper. As the solvent soaks along the paper, the components are absorbed to different extents and thus move along the paper at different rates. In column chromatography the components separate out along a column of a powdered absorbent, such as silica or aluminium oxide.
n. an organic compound that is an intermediate in many bacterial fermentations and is produced by fatty acid oxidation. In certain abnormal conditions (for example, starvation) acetone and other *ketones may accumulate in the blood (see ketosis). Acetone is a volatile liquid that is miscible with both fats and water and therefore of great value as a solvent. It is used in chromatography and in the preparation of tissues for enzyme extraction.... acetone
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