By different separation mechanisms, there are:

• Adsorption chromatography 

Adsorption chromatography is the oldest type of chromatography technique. It makes use of a mobile phase which is either in liquid or gaseous form. The mobile phase is adsorbed onto the surface of a stationary solid phase.

• Partition chromatography

In Partition chromatography solutes are separated based on their partitioning between a liquid mobile phase and a stationary phase coated on a solid support. The support used in partition chromatography is usually silica but can also be other materials.

• Ion exchange chromatography 

Ion exchange chromatography separates the components of a mixture based on their charge, in addition to or instead of their size. In essence, positively (cations) or negatively (anions) charged ions are separated using different stationary phases and different pH mobile phases.

• Size exclusion chromatography (SEC) 

Size exclusion chromatography (SEC) separates molecules based on their size by filtration through a gel. The gel consists of spherical beads containing pores of a specific size distribution. Separation occurs when molecules of different sizes are included or excluded from the pores within the matrix. Small molecules diffuse into the pores and their flow through the column is retarded according to their size, while large molecules do not enter the pores and are eluted in the column's void volume. Consequently, molecules separate based on their size as they pass through the column and are eluted in order of decreasing molecular weight (MW).

By different physical states of mobile phase, there are:

• Gas chromatography

In gas chromatography the mixture of interest is vaporized and carried through a stationary phase (usually a metal or glass separation column) with an inert gas, usually nitrogen or helium. Larger molecules in the mixture take longer to pass through the column and reach the detector at the far end.

• Liquid chromatography

In liquid chromatography, the mixture of interest is dissolved in a liquid and passed through a solid stationary phase, which is often made of a silica material. Several varieties of liquid chromatography exist, depending on the relative polarities of the mobile and stationary phases (normal-phase versus reverse-phase) and whether the mobile phase is pressurized (high-performance).

• Supercritical fluid chromatography

In Supercritical fluid chromatography the mobile phase is a fluid above and relatively close to its critical temperature and pressure. If a liquid or a gas is used above its critical temperature and pressure, it changes to a supercritical fluid. The characteristics of supercritical fluids are intermediate between those of gases and liquids. The lower viscosity and high diffusivity in comparison to a liquid make supercritical fluids achive faster stationary phase–mobile phase mass transfer, while the higher density, in comparison to a gas, allows the solubilization and transport of the solutes through the column at lower temperatures.

• Capillary Electrochromatography (CEC)

In Capillary Electrochromatography the mobile phase is driven through the chromatographic bed by electroosmosis. Capillary electrochromatography is a combination of two analytical techniques, high-performance liquid chromatography and capillary electrophoresis. Capillary electrophoresis aims to separate analytes on the basis of their mass-to-charge ratio by passing a high voltage across ends of a capillary tube, which is filled with the analyte. In capillary electrochromatography capillaries, packed with HPLC stationary phase, are subjected to a high voltage. Separation is achieved by electrophoretic migration of solutes and differential partitioning.

By chromatographic bed shape, there are:

• Thin-layer chromatography (TLC)

In thin-layer chromatography (TLC), the stationary phase is a thin layer of solid material, usually silica-based, and the mobile phase is a liquid in which the mixture of interest is dissolved. Thin-layer chromatography comes with the advantage of photographing well, making its output easy to digitize.

• Column chromatography

In column chromatography the stationary bed is within a tube. The particles of the solid stationary phase or the support coated with a liquid stationary phase may fill the whole inside volume of the tube (packed column) or be concentrated on or along the inside tube wall leaving an open, unrestricted path for the mobile phase in the middle part of the tube (open tubular column). Differences in rates of movement through the medium are calculated to different retention times of the sample.

• Paper chromatography

Paper chromatography involves placing a small dot or line of sample solution onto a strip of chromatography paper. The paper is placed in a container with a shallow layer of solvent and sealed. As the solvent rises through the paper, it meets the sample mixture, which starts to travel up the paper with the solvent. This paper is made of cellulose, a polar substance, and the compounds within the mixture travel further if they are less polar. More polar substances bond with the cellulose paper more quickly, and therefore do not travel as far.

Choice of Chromatography Methods

Among all methods to use chromatography to separate compounds, the choice of methods lies in the physicochemical characteristics of the molecule to be separated. The solid phases used for chromatography, also called chromatography media, are porous inert supports and can be functionalized with various chemical groups to dictate the interactions with the molecules to be separated. 

In applicaiton, sensible choice of right solid phase or packing material is the core of Chromatography, for it plays a significant role in the results and efficiency of extraction and purification process. Silica gel is one of the most versatile and effective packing material in chromatography and is also one of the most popularly and widely used in fields like modern biomedicine, life science, fine chemistry, analytical chemistry, organic chemistry, biochemistry, food safety, plant extraction, scientific analysis, environement mornitoring, petrochemicals etc.,

Silica gel is a polar absorbent with slight acidity. It absorbs components in a mixture and can meanwhile remain neutral and maintain its own structure in the due process. Silica based packing material also features high mechanical strength and can endure high pressure and speed.   Silica-based packing material produced by Qingdao Bangkai is newly developed by its R&D centre and is with higher purity and lower metal content, and bonded with multiple functional groups, and has higher reproducibility and load capacity. One of Bangkai’s newly developed silica-based packing material has been sucessufly validated to be used in electro-optical products. It can be customized upon request and is the ideal choice for the improvement of separation&purification process and repalcement of similiar products in the international market.

Referrence: WIKIPEDIA 

https://en.wikipedia.org/wiki/Chromatography