Liquid partition chromatography:

In liquid-liquid partition chromatography, there is a support which holds the stationary liquid phase and a mobile liquid phase runs over it. Because of the requirement that the two liquids be immiscible, that follows in which they differ markedly within polarity. Either the more polar or less polar may be immobilized. Most commonly, a polar solvent is held on the support. This is called reversed phase chromatography if a non polar solvent is held after making the support hydrophobic,.  The components of the mixture redistribute themselves in the two liquid phases resulting into separation. It is in some ways similar to liquid-liquid extraction discussed above. If the support material is packed in a column, the method is known as column liquid-liquid partition chromatography. The explanation of this method is elaborates in Unit 5 of this course. A simpler version of this method is available within the form of planar or 2D chromatography. The support is either a thin layer of inert material coated over a glass plate or a chromatographic paper. And therefore, we have two categories of 2D chromatography: thin layer chromatography and paper chromatography. In these two cases, a mobile phase could be made to move either from top to bottom or bottom to top and, therefore, there are two modes of operations descending and ascending chromatography. The details of planar chromatography are elaborates in Unit 6 of this course.

An improved version of liquid chromatography is in the form of high performance/ high pressure liquid chromatography (HPLC). It is one of the most hugely used separation methods. The particle size of the packing material is much smaller and a high pressure around 6000 psi is applied at the top of the column. A high pressure version of thin layer (HPTLC) is also available. Unit 8 of this course incorporates the details of this technique.

In gas-liquid chromatography, the stationary phase is a liquid coated in a column or on a support packed in the column. The mobile phase is a carrier gas that carries along with it the sample in form of a gas. The sample is volatilized to be carried through. The partitioning takes place among the carrier gas and the coated liquid.