Chemistry

Image of molecule from csus.edu
Image edited by Lap

Chromatography

Chromatography is a method in which a mixture is separated into components between two phases. This allows analysis of the sample and the chemical reaction. The two phases are stationary and mobile phases. The stationary phase remains in place, while the mobile phase carries the components through the medium. The components of the mixture move in different speeds based on their solubility and affinity to the stationary phase.

Thin layer chromatography

One way to separate the mixture for analysis is thin layer chromatography (TLC). TLC has a layer of silica gel (stationary phase), which acts as an absorbent because of its large surface area for interacting of molecules, over a plate of plastic. Silica gel has a very polar surface because of the –OH bond, which can form hydrogen bonds, van der waals, and dipole-dipole interactions. Mixtures or compounds are blotted into the TLC plate and a solvent (mobile phase) is added. As the solvent travels up the plate due to capillary force, the compound will move up by constantly absorbing to the surface and dissolve back to the solvent. Due to the compounds’ different polarities, they will travel up at different rates. The more polar the compound is, the more affinity it has for the stationary phase and will travel less distant than a less polar compound. 

Column Chromatography

Another method is column chromatography, which works in a similar way but mixture can be completely separated into components. Instead of using a TLC plate, a column filled with silica gel is used. The less polar compounds travel down faster than a more polar compound. Therefore, a less polar solvent is used at first, then a more polar solvent is used for later fractions to get the more polar compounds out.

Gas chromatography

Gas chromatography is another method to analyze samples by separation. Gas chromatography separates the components by volatility and the molecules travel through a column with the help of helium. Higher volatility travels faster than low volatility components.

High performance liquid chromatography

Last is the liquid chromatography and the high performance liquid chromatography (HPLC). HPLC consist of a pump that moves the mobile phase and mixture through the column and a detector that analyzes the sample, such as spectroscopy. 

Using these methods, a sample mixture can be separated into individual components in which we could identify, quantify, and purify.