About C18 and C8 HPLC Column.
- C18 is octyl decyl silane (ODS), that contains 18 carbons bound to the silica. So C18 have more carbons & a longer carbon chain than usually C8 (contain 8 carbons) or C4 (contain 4 carbons).
- Having extra carbons chain, C18 has a larger surface area and more denser so that the mobile phase has to travel across more.
- This leads to more interaction time between the bonded phase of the column and the elutes traveling through a mobile phase. As a result, the sample (Analyst) elutes more slowly and gives more separation.
- C18 column is based on hydrophobic interaction mechanism.
- C18s are good for long-chain fatty acids and complex molecules.
Related: Difference Between Stationary Phase and Mobile Phase
Examples of C18 Column Used in Pharmaceutical Widely:
- Zorbax C18 by Agilent
- Allure® C18 by Restek
- Symmetry® C18 by Waters
- Superspher® 100 RP-18e by Merck
- Hypersil® ODS by Thermo/Hypersil
- Luna® C18 by Phenomenex
Related: Number of theoretical plates (N), Resolution (RS), Column Storage, Column Cleaning and Regeneration of HPL column.
- Other hand, C8 (also known as octadecyl) is better for shorter retention time (RT) and delivers sharper peaks in HPLC. C8 column types are mainly used in small organic compounds.
Related: What is Stationary phase in HPLC ?
Examples of C8 Columns Used in Pharmaceutical widely:
- Hypersil™ PREP HS C8 HPLC Columns by Thermo Scientific
- Symmetry C8 Column by Waters
- Luna C8 by Phenomenex
Related: Principle of HPLC
Summary in C18 and C8 Difference:
- C18 – octyl decyl silane (ODS), C8- octadecyl chain
- C18 having more carbon chain than C8 column
- C18 is more denser than C8
- C18 is more hydrophobic than C8
- C18 column take more retention time than C8 column.
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