Gradient Elution of Plan Components (Hexane-Soluble Extract)
Column Chromatography ________________________________________________
You have already performed two chromatography experiments: gas chromatography and thin layer chromatography. All chromatography experiments involve passing a mixture of analytes through a system that includes a mobile phase and a stationary phase. The partitioning of the analytes between these two phases determines the rate at which they pass through the system, and (in theory) allows them to be separated from one another. Column chromatography is a technique routinely used by organic chemists to separate sometimes complicated mixtures of compounds. For example, a chemical reaction may produce more than one compound and the products must be separated. In other instances, if a reaction does not go to completion, i.e. the starting materials do not react completely, then leftover reactants must be separated from the products of interest. Column chromatography is also used to separate mixtures of naturally occurring compounds isolated from plants and other living organisms. Performing column chromatography involves packing a column, which is a glass cylinder, with the stationary phase. The stationary phase is typically silica “gel” or powdered alumina, depending on the types of compounds you wish to separate. The mixture is placed on top of the packing material and a steady, continuous flow of eluting solvent is passed through the column. Although in the TLC experiment only one developing solvent is used to develop a plate, this is not the case for column chromatography: we can switch solvents in the middle of the process. A typical column chromatography experiment would involve starting with a less polar solvent; then, as the non-polar components of the mixture are eluted from the column, one can change to a more polar solvent to move the more polar compounds off the column as well. The polarity of a solvent mixture can be easily adjusted simply by changing the proportions of each of the
You have already performed two chromatography experiments: gas chromatography and thin layer chromatography. All chromatography experiments involve passing a mixture of analytes through a system that includes a mobile phase and a stationary phase. The partitioning of the analytes between these two phases determines the rate at which they pass through the system, and (in theory) allows them to be separated from one another. Column chromatography is a technique routinely used by organic chemists to separate sometimes complicated mixtures of compounds. For example, a chemical reaction may produce more than one compound and the products must be separated. In other instances, if a reaction does not go to completion, i.e. the starting materials do not react completely, then leftover reactants must be separated from the products of interest. Column chromatography is also used to separate mixtures of naturally occurring compounds isolated from plants and other living organisms. Performing column chromatography involves packing a column, which is a glass cylinder, with the stationary phase. The stationary phase is typically silica “gel” or powdered alumina, depending on the types of compounds you wish to separate. The mixture is placed on top of the packing material and a steady, continuous flow of eluting solvent is passed through the column. Although in the TLC experiment only one developing solvent is used to develop a plate, this is not the case for column chromatography: we can switch solvents in the middle of the process. A typical column chromatography experiment would involve starting with a less polar solvent; then, as the non-polar components of the mixture are eluted from the column, one can change to a more polar solvent to move the more polar compounds off the column as well. The polarity of a solvent mixture can be easily adjusted simply by changing the proportions of each of the