Mobile phase in chromatography

MD.JABIUR RAHAMANDAFFODIL INTERNATIONL UNIVERSITY,BANGLADESH

DEPT. OF PHARMACY

Chromatography is a method by which a mixture is separated by distributing its components between two phases. The stationary phase remains fixed in place while the mobile phase carries the components of the mixture through the medium being used. The stationary phase acts as a constraint on many of the components in a mixture, slowing them down to move slower than the mobile phase. The movement of the components in the mobile phase is controlled by the significance of their interactions with the mobile and/or stationary phases. Because of the differences in factors such as the solubility of certain components in the mobile phase and the strength of their affinities for the stationary phase, some components will move faster than others, thus facilitating the separation of the components within that mixture.

Mobile phase in Gas Chromatography

A gas chromatograph is a chemical analysis instrument for separating chemicals in a complex sample. A gas chromatograph uses a flow-through narrow tube known as thecolumn, through which different chemical constituents of a sample pass in a gas stream (carrier gas, mobile phase) at different rates depending on their various chemical and physical properties and their interaction with a specific column filling, called the stationary phase. As the chemicals exit the end of the column, they are detected and identified electronically. The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time (retention time). Other parameters that can be used to alter the order or time of retention are the carrier gas flow rate, column length and the temperature.

Mobile phase in TLC

They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase and carries the components of the mixture with it.

Mobile Phases in Reverse Phase chromatography

In reverse phase applications water is usually the base solvent. Other polar solvents such as Methanol, Acetonitrile or Tetrahydrofuran are added in fixed or varying proportions. pH is adjusted by buffers to modify separations of ionizable solutes. Ion-pairing reagents also enhance separation selectivity of charged analytes by increasing retention on hydrophobic bonding phases.

Mobile Phases in Normal Phase Chromatography

Typically non polar solvents such as hexane, heptane, iso-octane are used in combination with slightly more polar solvents such as isopropanol, ethyl-acetate or chloroform. Retention increases as the amount of non polar solvent increases in the mobile phase.

Mobile Phases in Ion Exchange Chromatography

Aqueous salt solutions are generally used as mobile phases. Moderate amounts of water miscible polar organic solvents such as methanol can be added to buffered mobile phases. Solvent strength and selectivity can be adjusted by control of pH, buffer and salt concentrations.

Mobile Phases for Size Exclusion Chromatography

• The mobile phase composition is not varied as the detector is sensitive to such changes.

• Choice of mobile phase is dependent on its ability to dissolve sample and maintain consistent viscosity at operating temperature. High polarity solvents such as acetone, alcohols, DMSO and water are not used with polystyrene packings. Ionic strength is maintained by addition of salts.

Mobile phase in paper chromatography

The stationary phase of paper chromatography is filter paper, and the mobile phase is an organic solvent or mixture. A small drop of the liquid mixture is placed at one end of the paper. The end of the paper is then immersed in a solvent. As the solvent moves up the paper, any molecules in the mixture that are soluble in the solvent will move with the solvent. Based on their solubility to the mobile phase and attraction to the stationary phase, some molecules will move faster than others. Each different molecule in the mixture will move at a different speed and will be at a different position on the finished chromatogram.