Column Chromatography

Column chromatography is a preparative method for separating and isolating compounds from mixtures which can later be analyzed using thin-layer chromatography (TLC), gas chromatography, or IR. The method is used for obtaining compounds from natural sources or for purifying products from reaction mixtures. This method can be considered an upside-down version of TLC. Instead of having a thin layer of adsorbent attached to a solid support, a column is filled with a larger amount of adsorbent, often silica gel, and the mixture is loaded on top of it. While TLC depends on capillary action, column chromatography depends on a solvent or eluent moving down the column using the force of gravity. As this eluent moves down the column, it carries the soluble compounds with it and compounds having strong interactions with the adsorbent move more slowly than compounds having weaker interactions with the adsorbent. By taking advantage of the material used for the stationary and mobile phase, the compounds will separate in distinctive bands and each band will come out of the column individually. This will allow for the collection of each separate band in different vials which can then be analyzed with TLC and then dried to later be analyzed based on their melting points.
Polarity plays a large role in the process, where the using a non-polar solvent allows for a non-polar substance to be collected first before the more polar components. As the polarity of the solvents increase, more polar compounds travel further faster. This is why it is important for the solvents used to slowly change in polarity throughout the column chromatography procedure for better separation.[