There won't be as much attraction between the hydrocarbon chains attached to the silica (the stationary phase) and the polar molecules in the solution. In this case, there will be a strong attraction between the polar solvent and polar molecules in the mixture being passed through the column. A polar solvent is used - for example, a mixture of water and an alcohol such as methanol. In this case, the column size is the same, but the silica is modified to make it non-polar by attaching long hydrocarbon chains to its surface - typically with either 8 or 18 carbon atoms in them. The non-polar ones will therefore pass more quickly through the column. Polar compounds in the mixture being passed through the column will stick longer to the polar silica than non-polar compounds will. A typical column has an internal diameter of 4.6 mm (and may be less than that), and a length of 150 to 250 mm. The column is filled with tiny silica particles, and the solvent is non-polar - hexane, for example. Although it is described as "normal", it isn't the most commonly used form of HPLC. This is essentially just the same as you will already have read about in thin layer chromatography or column chromatography. These methods are highly automated and extremely sensitive.Ĭonfusingly, there are two variants in use in HPLC depending on the relative polarity of the solvent and the stationary phase. The other major improvement over column chromatography concerns the detection methods which can be used. This allows a much better separation of the components of the mixture. It also allows you to use a very much smaller particle size for the column packing material which gives a much greater surface area for interactions between the stationary phase and the molecules flowing past it. Instead of a solvent being allowed to drip through a column under gravity, it is forced through under high pressures of up to 400 atmospheres. High performance liquid chromatography is basically a highly improved form of column chromatography. Use the BACK button on your browser to return quickly to this page. HPLC is essentially an adaptation of column chromatography - so it might be a good idea to have a (very quick) look at that as well. High performance liquid chromatography works on the same basic principle. Note: It is important to read the introductory page about thin layer chromatography before you continue with this one - particularly the part about how thin layer chromatography works. This page looks at how it is carried out and shows how it uses the same principles as in thin layer chromatography and column chromatography. High performance liquid chromatography is a powerful tool in analysis. HIGH PERFORMANCE LIQUID CHROMATOGRAPHY - HPLC High performance liquid chromatography - hplc
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