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| Dyer Scientific and Technical Translations | |
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CHROMATOGRAPHY 1. Introduction 2. Paper Chromatography 3. Thin-layer Chromatography 4. Column/Liquid Chromatography 5. Gas Chromatography 6. High_Pressure Liquid Chromatography 7. Glossary 8. References |
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| Column Chromatography; Liquid Chromatography All the forms of chromatography other than paper and thin-layer chromatography use columns; but "column chromatography" and "liquid chromatography" typically mean the early form in which the stationary phase, adsorbed on a solid "support" to produce a "packing", is packed into a glass tube about 20 mm in diameter and about 200-300 mm long. The "packing" is often packed, literally, by tamping it with a glass rod. The sample is applied to the top of that column, and then mobile phase is allowed to flow through the column (gravity flow). The original stationary phase was water adsorbed to particles of the solid, which may be powdered sugar, powdered cellulose, or many other possibilities. If there are colored components, one can watch them separating. It is possible to stop the solvent flow, push the packing out of the column, and cut out a colored segment to recover that component. Usually, though, the flow is continued, perhaps overnight, so that all the components "elute" from the column into a fraction collector. That is typically a turntable holding perhaps 100 test tubes in a spiral pattern. A motor rotates the turntable to place a new test tube below the column at intervals. The intervals are determined by a timer, by a drop counter, or by a siphon which collects a fixed volume and then dumps it into a tube. Tubes containing components of interest are located by color, ultraviolet absorption, fluorescence, chemical reactions, etc. This form of chromatography has become less important with development of high-pressure liquid chromatography, but it can handle much larger amounts of material. Reports and procedures should specify at least the solvent mixture and
packing material. Back to top |