Tips for sample loading of column chromatography
Sample loading can also be divided into wet method and dry method:
The wet method generally uses eluent to dissolve the sample, and can also use methylene chloride, ethyl acetate, etc., but the less solvent, the better. Then transfer the obtained solution with a rubber tip dropper and add it slowly and evenly along the inner wall of the chromatography column. If sea sand is not used, try not to damage the silicone surface. After adding the sample, open the piston at the bottom of the column to allow the stationary phase to fully absorb the added sample. Then add some eluent, and after sufficient adsorption, plug a ball of absorbent cotton close to the silica gel surface. You can then safely add large amounts of eluent without damaging the silicone surface. Many samples are sticky before loading onto the column, which is generally okay. Sometimes it will precipitate on the silica gel after loading the sample. This usually occurs when a relatively large number of samples are used.
This is because the adsorption of the sample by the silica gel is saturated, and the sample itself is a relatively good solid before it precipitates. This requires recrystallizing the sample first to obtain most of the product and then column separation of the remaining product. It doesn't matter if recrystallization is not possible, just pass it through the column. The sample will slowly dissolve as the eluent flows, and finally flow out with the eluent. Some samples have poor solubility, and the solvents that can dissolve them cannot be loaded onto the column (such as DMF, DMSO, etc., which will travel with the solvent, and the color development will have a long tail). In this case, the dry method must be used to load the column.
In the dry column method, the sample to be separated is dissolved in a small amount of solvent, then a small amount of silica gel is added, the mixture is mixed thoroughly, and then the solvent is removed. Generally, the sample and silica gel are mixed at a ratio of 1:1. The amount of silica gel used can also be less, but it must be ensured that no obvious solid particles can be seen after spin drying, so that the sample is adsorbed on the surface of the silica gel. Then carefully add it to the packed column and add eluent for elution.
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