Several Tips on Using Column Chromatography Silica Gel
In organic experiments, when a mixed sample containing a variety of organic compounds cannot be recrystallized, column chromatography on silica gel can be said to be an effective separation method. In the laboratory, stationary phase adsorption columns are usually made of silicon and alumina. The separation principle of silica gel chromatography is based on the adsorption force of substances to silica gel.
Many experimental books on column chromatography silica gel chemistry describe the experimental methods of main layer analysis, but most of them are general descriptions, and some descriptions are not applicable in the laboratory. For example, many books mention that when installing columns, first spread quartz sand on the bottom, pour it into a fixed table, and then spread quartz sand on top. It is not suitable for laboratories. Based on many years of experience in using column chromatography silica gel, some tips for using column chromatography silica gel have been summarized.
1. Use silica gel column chromatography.
Ultra-short layers are prone to long or short columns, and sometimes a large amount of silicon remains, resulting in a waste of silicon. This is mainly due to the uncertainty in the usage of stationary phases such as silicon. The silicon used for column analysis is generally 100-200 mesh. The mass of 100 ml of silicon is about 47 grams. A column with a diameter of 2.8 cm can accommodate a height of 18 cm.
2. Use eluent.
Chromatography silica gel can sometimes see the separation effect on a thin layer, but it is difficult to separate when passing through column chromatography silica gel. The main reason is that the silicon used for thin layer analysis is much finer than the silicon used for column analysis, so the separation effect is very good. The solution is to make the tax system less polarized. Generally, the detergent used for column chromatography silica gel analysis has twice the polarity of the revealing agent used for thin layer analysis, which can achieve better separation results. When the polarity range of the separated substance is large, gradient elution can be used to gradually increase the polarity of the solvent and wash away other compounds adsorbed on the silica gel one by one.