Difference between stationary phase and mobile phase in chromatography

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Chromatography-an analytical tool for separating a mixture into its constituent components. These components are separated on the basis of their relative distribution between the two phases. What are these two phases? What is the difference between the two? How each of these two phases performs its particular function in carrying out a successful chromatographic separation? All these questions form the primary focus of this article.

What is stationary phase

Stationary phase is the phase that stays fixed in its place. During chromatography, it provides a surface for the solvent carrying the analyte components to move over it. The solute components strongly interactive with the stationary phase gets retained on it. A chromatographic stationary phase could either be a solid or a liquid coated on a solid support.

What is mobile phase

Mobile phase is the phase that flows over the stationary phase. It carries the analyte components with it on the basis of their solubility in the mobile phase. A chromatographic mobile phase could either be a liquid or a gas.

After reading those, you can come back here and do a quick revision using the table given below. The table specifically highlights the differences between a stationary phase and a mobile phase in chromatography.

Difference between stationary phase and mobile phase

PropertyStationary PhaseMobile Phase
Appearance Stays fixed on a plane or in a columnFlows over the stationary phase
Physical StateSolid or Liquid coated on solid supportLiquid or Gas
CompositionA single composition of the stationary phase is maintained throughout the chromatographic processThe mobile phase composition can vary via gradient elution when performing a chromatographic separation
Interaction with the analyte componentsInteracts with and retains analyte components on the basis of affinity, size, shape, charge and chemical bonding etc.Sweeps the analyte components on the basis of solubility
Analyte recoveryAnalyte components strongly retained onto the stationary phase, move slowly with the mobile phase and elute out laterAnalyte components with high solubility in the mobile phase moves quickly thus faster elution
Type of chromatographyOn the basis of stationary phase, chromatography can be classified into solid-liquid chromatography, gas-solid chromatography and/or liquid-liquid chromatographyOn the basis of mobile phase, chromatography can be classified into liquid-liquid chromatography, gas-liquid chromatography or gas-solid chromatography
PolarityA more polar stationary phase than the mobile phase gives chromatography its name: normal phase chromatographyA chromatographic separation in which the mobile phase is more polar than the stationary phase is called reverse phase chromatography

Having discussed the generally differences between a stationary phase and a mobile phase in chromatography, we can highlight the differences between the two for specific types of chromatography as shown in the table below.

Type of ChromatographyStationary PhaseMobile Phase
Paper ChromatographyWater trapped in the cellulose layers of the paperOrganic solvents (ethanol, methanol, n-hexane etc.)
Thin Layer Chromatography
(TLC)
Silica gel or alumina coated on a glass plateOrganic solvents
High Performance Liquid Chromatography
(HPLC)
Silica packed in a column (Normal phase)
C-8 or C-18 modified silica packed in a column
(Reverse phase)
A combination of organic solvents
(such as ethanol, methanol, acetonitrile, chloroform and benzene etc.) and their aqueous solutions
Single composition throughout (Isocratic elution)
Varying solvent composition (Gradient elution)
Gas Chromatography
(GC)
Silica packed column
or
Liquid coated capillary columns
Inert carrier gas such as helium used as mobile phase
Ion Exchange ChromatographyCation exchanger
or
Anion exchanger
Salt solutions
Molecular
or
Size Exclusion Chromatography
Porous substances such as silica gelOrganic solvents
Affinity Chromatography 
Silica support with a specific ligand
A solution containing a complementary ligand that binds more strongly with the stationary phase than the analyte molecules

The diagrammatic representation below illustrates a detailed column chromatographic separation using both the stationary phase and the mobile phase.

Conclusion

Thus concluding, the stationary phase as well as the mobile phase are the essential separating media of a chromatographic process. Chromatography cannot be performed in the absence of any of the two phases. Both hold their distinction in terms of appearance, properties, nature and function.

We have for now studied the basics of chromatography in a detailed perspective. The upcoming articles of the series will particularly focus on different types of chromatography in further detail with more insightful information, one at a time.

You can read extensively about what is a stationary phase and what is a mobile phase in chromatography from our separate articles on the topics.

References

1.  Calderon, L. d. A. (2016). Chromatography: The Most Versatile Method of Chemical Analysis.

2. Danielson, N. D. (2003). Liquid Chromatography. Encyclopedia of Physical Science and Technology (Third Edition). R. A. Meyers. New York, Academic Press: 673-700.

Difference between stationary phase and mobile phase in chromatography

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