Difference between C8 and C18 column in HPLC

High-performance liquid chromatography is a method used to separate, identify, and quantity of each analyte in the complex mixture using a mobile phase. Both C8 and C18 refer to the bonded face of the alkyl chain and both are used in HPLC separation.

There are numerous different kinds of reverse phases there in the market, including C8 and C18 columns. C18 is the most popular one than a C8 column. C8 and C18 are both reversed-phase columns, both columns refer to the alkyl chain length of the bonded phase. The length of the chain affects the hydrophobicity of the sorbent phase and therefore increases the retention time of the component. C18 have the maximum amount of hydrophobicity, since the longer length of the carbon chain, C-18 is extra hydrophobic compared to the reverse phases.

C8 column is used while small RT is desired, if hydrophobicity is low, there is less retention time for non-polar analytes, therefore, the non-polar analytes or compounds separate out more quickly with C8 column. The C8 is select over the C18, in the reverse phase matrix where the degree of hydrophobicity is low. But, the C18 column is more accepted and broadly used because C18 silica gel interacts with the broad range of analytes, hence it used in the separation, qualitative and quantitative studies in the pharmaceutical industries, chemical analysis, and environmental science.

• C18: Octadecyl silane
• C8: Octyl silane
• In reverse phase HPLC: the mobile phase is polar and the stationary phase is non-polar.
• In normal phase HPLC: the mobile phase is non-polar and the stationary phase is polar.

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