The key difference between C8 and C18 column is that the C8 column has Octylsilane as the stationary phase whereas the C18 column has Octadecylsilane.
The C8 and C18 columns differ from each other according to the stationary phase. We use these columns in HPLC (high-performance liquid chromatography). The compounds we use in these columns have different alkyl chain lengths of silane compounds.
What is C8 Column?
C8 column is a form of column present in some HPLC apparatuses, and it has Octylsilane as its stationary phase. And, this compound in stationary phase has 8 carbon atoms in its alkyl chain. Further, it tends to retain components of the analyte less than that of the C18 column. Therefore, a compound will elute faster in a C8 column.
However, it is less dense because it has a less number of carbon atoms; the length of the carbon chain of this compound in stationary phase is short. Moreover, nonpolar compounds move down the column rapidly with C8 column. It is mainly because of the lower hydrophobicity of C8 compound.
What is C18 Column?
C18 column is also a form of a column that we use in HPLC apparatuses, and it has Octadecylsilane as its stationary phase. Octadecylsilane (in stationary phase) has 18 carbon atoms in its alkyl chain. Further, it tends to retain more components of the analyte when compared to C8 columns. The analyte will elute slower in this column.
Moreover, C18 is denser than a C8 column. And this increases the path length of the analyte through the column. Also, this allows the separation of more complex compounds. The retention time of this column is high. In addition, the hydrophobicity of the stationary phase is high. It allows the slow elution of nonpolar compounds through the column.
Applications of this type of columns are mainly in environmental science, pharmaceutical industries, chemical analysis, etc.
What is the Difference Between C8 and C18 Column?
C8 column is a form of column present in some HPLC apparatuses, and it has Octylsilane as its stationary phase. The C8 column shows a low retention time. Moreover, the analyte elutes faster in this column. It is because it has a less dense stationary phase. C18 column, on the other hand, is also a form of a column that we use in HPLC apparatus, but it has Octadecylsilane as its stationary phase. More importantly, this column shows a high retention time. In addition to that, the analyte elutes slowly in this column. It is because of the high dense stationary phase. The following infographic presents a detailed difference between C8 and C18 column as a side by side comparison.
Summary – C8 vs C18 Column
C8 and C18 are two different columns that we can use in an HPLC apparatus. The key difference between C8 and C18 column is that the C8 column has Octylsilane as the stationary phase whereas the C18 column has Octadecylsilane as the stationary phase.
1. Choudhary, Ankur. “Difference between C8 and C18 Columns Used in HPLC System.” Pharmaceutical Guidelines, Pharmaceutical Guideline, 5 Aug. 2011. Available here
2. “C18 Column / C18 HPLC Columns.” Labcompare. Available here