Difference Between C18 Column And C8 Column

C18 chromatographic columns are usually divided into three parts:

1. Octadecyl: It is the bonding phase, in addition to octadecyl, there are octadecyl, butanyl, phenyl, fluorophenyl, etc.;
2. Silane bonding: that is, the bond and the method, usually the bonding phase is bonded by the chemical reaction between the silanizing agent and the silanol group on the surface of the silica gel, so it will be called silane bonding;
3. Silica gel: It is the filler matrix.

There are often some doubts when choosing imported C18 chromatographic columns or C8 chromatographic columns.

What they have in common:
Both C8 and C18 are a kind of reversed-phase column, which are suitable for analyzing weakly polar substances.

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The difference between the two structures:

C8 is a silica-bonded octadecyl group, and C18 is a silica-bonded octadecyl group. In comparison, the polarity of C18 is smaller than that of C8. C8 is on the side with stronger polarity and C18 is on the side with weaker polarity. That is to say, C8 is suitable for the analysis of slightly more polar substances in weakly polar substances, and C18 is suitable for the analysis of weaker polar substances in weakly polar substances. This is the difference in their polarity, but the difference is not particularly obvious. Generally, substances that can be analyzed by C8 can also be separated on C18. This is because the latter has better retention properties than the former, which seems to be more closely related to the structure of the column packing.

C18 has a longer carbon chain than C8 and therefore brings better retention properties. Therefore, C8 is more suitable for the analysis of macromolecular substances, such as some globulins, etc., and C8 and buffer salt eluent are used together. Conversely, substances with smaller molecular weights are often analyzed and separated using C18.

The retention performance of the C18 chromatographic column is stronger than that of C8, and the carbon content has a great influence on the separation effect and the retention time of the main components, so the higher the carbon content, the longer the retention time of the main components.

The difference between the two uses:
C18 column is suitable for: acid, alkali, neutral, polar, medium polar, and non-polar sample analysis.
The C8 column is suitable for: lipids, steroids, analytes with high hydrophobicity, and samples with different hydrophobicity.

The essential difference between the C8 column and the C18 column
For the C8 column and C18 column, I believe that many people are confused, sometimes even confused, it is true that the C8 column is silica-bonded octadecyl, and the C18 column is silica-bonded octadecyl. Regardless of the difference between the words, the difference will also be different.

In contrast, C18 has a stronger analyte retention performance than C8, and the carbon content has a great influence on the separation effect and the retention time of the main components. Therefore, the higher the carbon content, the longer the retention time of the main components. Both C8 and C18 columns are a type of reversed-phase column. The principle of chromatographic separation is similarity and compatibility, and here is the difference in polarity.

C8 is on the weaker side with stronger polarity, while GD’s new series C column features: high surface coverage and thorough double end-capping, which improves the stability of column separation; Optimal separation efficiency for the analysis of acidic and basic, and chelated compounds. GD’s new series of C8 chromatographic columns have a variety of pH values ​​ranging from 0.5-8.0, 1.0-10.0, 2-11.5… To meet the chromatographic analysis of different conditions, tailing phenomenon usually occurs for strong basic compounds, GD new series C8 chromatographic column still has good symmetrical peak shape and high column efficiency for analysis; showing such greatest advantages, it is undoubtedly an excellent choice for GD new series C8 chromatographic column for routine analysis; excellent batch Batch and column-to-column reproducibility; applicable to all sample size ranges from analysis to preparation for multicomponent systems.

The C18 chromatographic column is on the weaker side of the polarity, but on the issue of steric hindrance, due to the difference in the C chain, the C18 chromatographic column can play a better role and retain better characteristics.

a. Different filling materials

1. C18 chromatographic column: The alkane bonded to the silica gel is 18 carbons and packed with C18.
2. C8 chromatographic column: The alkane bonded to the silica gel is 8 carbons, and the packing is C8.

b. Different polarities

1. C18 chromatographic column: C18 is on the weaker side.
2. C8 chromatographic column: C8 is on the weaker side with stronger polarity.

c. the effect is different

1. C18 chromatographic column: suitable for analyzing weaker polar substances. Substances with smaller molecular weights are often analyzed and separated with C18.
2. C8 chromatographic column: analyze the slightly more polar substances in the weak polar substances. Since C18 has a longer carbon chain than C8, it brings better retention properties. Therefore, C8 is more suitable for the analysis of macromolecular substances, such as some globulins, etc., and C8 and buffer salt eluent are used together.