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Key Differences Between C8 and C18 Columns You Must Know

Key Differences Between C8 And C18 Columns

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Have you ever wondered how scientists untangle complex mixtures into their individual components? Well, high-performance liquid chromatography (HPLC) is a powerful technique that achieves just that. And at the heart of this process lies a critical element: the HPLC column.

What Different C8 or C18 HPLC Colum

Main Difference for the C8 Column and C18 Column, we will check as following factors: 

 1.Chemical Composition 2. Retention and Separation Efficiency, Hydrophobicity and Polarity; Sample Compatibility; Mobile Phase Considerations; Practical Considerations etc

So for electing the right HPLC column is like picking the perfect key for a specific lock. Different column types exist, each tailored to interact with various sample components in unique ways. Choosing the right one ensures optimal separation, allowing you to isolate and identify your desired compounds with precision.

As following, we will start to is make a detail explain for each factors.

1. Understanding C8 and C18 Columns

C8 and C18 columns are two titans in the world of HPLC stationary phases. Understanding their unique characteristics is crucial for selecting the right tool for your separation needs. Let’s delve into their definitions and applications:

C8 Columns: The All-Rounder

  • Definition: A C8 column features a silica surface modified with a layer of eight-carbon chains (octylsilane).
  • Characteristics: Compared to C18 columns, C8 has a shorter and less hydrophobic (water-repelling) stationary phase. This translates to:
    • Shorter retention times: Analytes spend less time interacting with the column, leading to faster separations.
    • Better suited for moderately polar analytes: Compounds with some polarity can navigate the C8 maze efficiently.
    • Reduced peak tailing: Sharper peaks on the resulting chromatogram, indicating cleaner separation.

C18 Columns: The Powerhouse for Non-Polar Separations

  • Definition: A C18 column boasts a silica surface bonded with eighteen-carbon chains (octadecylsilane).
  • Characteristics: The longer carbon chain in C18 offers a more hydrophobic environment with:
    • Stronger retention: Analytes interact more with the stationary phase, resulting in longer retention times.
    • Ideal for non-polar analytes: Compounds with minimal polarity find a strong affinity for the C18 surface.
    • Increased selectivity: The strong interactions can sometimes lead to better separation of very similar compounds.

Applications for Each Champion:

  • C8 Columns: Shine in separating moderately polar analytes like pharmaceuticals, natural products, and some biomolecules.
  • C18 Columns: Reign supreme for non-polar and hydrophobic analytes, including lipids, steroids, and fatty acids.

1.Chemical Composition

Bonded phases are chemically modified silica surfaces that form the stationary phase in HPLC columns. These modifications influence how analytes interact with the column, impacting separation efficiency.

Explanation of Octyl (C8) and Octadecyl (C18) Bonded Phases

Bonded PhaseDescription
Octyl (C8)Silica particles are bonded with a layer of eight-carbon chains (octylsilane). This creates a moderately hydrophobic environment.
Octadecyl (C18)Silica particles are bonded with a layer of eighteen-carbon chains (octadecylsilane). This creates a more hydrophobic environment compared to C8.

Impact of Carbon Chain Length on Column Performance

The length of the carbon chain in the bonded phase significantly affects column performance:

  • Hydrophobicity: Longer chains (C18) create a more hydrophobic environment, leading to stronger interactions with non-polar analytes and increased retention times.
  • Selectivity: C18 columns can sometimes offer better separation of very similar compounds due to the stronger interactions.
  • Retention times: C8 columns generally lead to faster separations due to the shorter carbon chain and weaker interactions with analytes.

2. Chemical Composition

The magic behind C8 and C18 columns lies in their bonded phases, which are chemically modified surfaces on the silica particles within the column. These modifications play a crucial role in how analytes interact with the column, ultimately affecting separation efficiency.

Unpacking the Bonded Phases:

  • Octyl (C8): Here, the silica surface is adorned with a layer of eight-carbon chains, known as octylsilane. This creates a moderately hydrophobic environment, meaning it repels water to some extent.
  • Octadecyl (C18): In this case, the silica particles are bonded with a layer of eighteen-carbon chains (octadecylsilane). Compared to C8, this creates a much more hydrophobic environment, with a stronger aversion to water.

The Carbon Chain Length: A Tuning Fork for Performance

The length of the carbon chain in the bonded phase acts as a key tuning knob for column performance. Here’s how it impacts separation:

  • Hydrophobicity: As the chain length increases (C8 to C18), the overall hydrophobicity of the stationary phase gets stronger. This translates to a greater attraction for non-polar analytes, causing them to interact more with the column and leading to longer retention times.
  • Selectivity: The stronger interactions in C18 columns can sometimes lead to improved separation of very similar compounds. These subtle differences in interaction with the longer carbon chains can help distinguish even closely related molecules.
  • Retention Times: Due to the weaker interaction with analytes, C8 columns with their shorter chains generally result in faster separations. Analytes spend less time interacting with the stationary phase, leading to quicker elution through the column.

In a nutshell: The carbon chain length acts like a volume knob for hydrophobic interactions. A longer chain (C18) creates a more “sticky” surface for non-polar analytes, making them stay longer (increased retention). This can also provide finer control for separating similar compounds. However, for moderately polar analytes, a C8 column with its shorter chain might be a better choice for achieving faster analysis times.

3. Retention and Separation Efficiency

here is the graph:

Retention Time Differences on C8 and C18 ColumnsC8 ColumnC18 Column 
Retention Time Differences on C8 and C18 Columns

4. Hydrophobicity and Polarity

The magic behind C8 and C18 columns lies in their ability to separate compounds based on their hydrophobicity, or their aversion to water. Let’s delve into how the difference in hydrophobicity between these columns influences separation.

C8 vs. C18: A Tale of Two Hydrophobicities

  • C8 Columns: With their shorter eight-carbon chains, C8 columns offer a moderately hydrophobic environment. This means they can interact with both non-polar and moderately polar compounds, although to varying degrees.
  • C18 Columns: Boasting longer eighteen-carbon chains, C18 columns create a much more hydrophobic environment. This translates to a stronger attraction for non-polar analytes, with minimal interaction with water-loving (polar) ones.

Hydrophobicity’s Impact on Separation:

The difference in hydrophobicity between C8 and C18 columns significantly influences how they separate polar and non-polar compounds:

  • Non-polar Compounds: These find a strong home in C18 columns due to their shared aversion to water. They interact extensively with the long carbon chains, leading to longer retention times. Conversely, in C8 columns, non-polar compounds experience a weaker attraction, resulting in faster elution.
  • Polar Compounds: Being attracted to water, polar compounds have minimal interaction with the hydrophobic stationary phase of both C8 and C18 columns. However, the shorter chain length of C8 offers a slightly less hydrophobic environment. This can allow some moderately polar compounds to pass through the C8 column more readily compared to C18, where they might experience some unwanted retention.

5. Sample Compatibility

When it comes to HPLC analysis, choosing the right column goes beyond just hydrophobicity and retention times. Sample compatibility plays a crucial role in ensuring efficient separations and protecting your column from damage. Here’s how C8 and C18 columns differ in their compatibility with various sample types:

C8 Columns: A More Versatile Approach

  • Strengths: C8 columns offer broader compatibility with a wider range of sample polarities. Their moderately hydrophobic environment allows them to handle both non-polar and moderately polar analytes to some extent.
  • Considerations: While C8 can handle moderately polar analytes, highly polar compounds might still experience some retention, potentially affecting separation efficiency. Additionally, for highly non-polar samples, C8 might not provide the strongest retention needed for optimal resolution.

C18 Columns: Powerhouse for Non-Polar Samples

  • Strengths: C18 columns excel in compatibility with non-polar samples due to their highly hydrophobic nature. This strong attraction leads to excellent retention and separation of these analytes.
  • Considerations: The strong hydrophobicity of C18 can be a double-edged sword. Highly polar compounds might get excessively retained, leading to peak broadening and potential column damage. Additionally, samples with high ionic content might interact with the silica base of the C18 column, affecting peak shapes and column lifetime.

Choosing the Right Match:

Here’s a breakdown to help you select the most compatible column for your sample:

  • Non-polar Samples: C18 is the clear winner, offering excellent retention and separation.
  • Moderately Polar Samples: C8 can be a good choice, providing a balance between retention and elution. However, for highly polar analytes within this range, consider alternative columns with more hydrophilic properties.
  • Highly Polar Samples: Neither C8 nor C18 is ideal. Opt for columns with more polar stationary phases designed for these types of analytes.

Additional Considerations:

  • Sample Solvents: The solvents used to dissolve your sample can also impact compatibility. Ensure the solvents are compatible with the column chemistry to avoid unwanted interactions or column degradation.
  • Sample Matrix: Complex sample matrices with a mix of polarities might require additional sample preparation or specialized column chemistries to achieve optimal separations.

By understanding the compatibility between your sample and the column, you can

6. Mobile Phase Considerations

The mobile phase in HPLC plays a vital role in analyte separation, and its composition can be significantly influenced by the choice of your column. Here’s a breakdown of the mobile phase considerations for C8 and C18 columns, highlighting their impact on method development and optimization:

C8 Columns: A More Flexible Dance with Mobile Phases

  • Mobile Phase Range: C8 columns offer a wider range of compatibility with mobile phases. You can utilize both higher aqueous percentages (more water) and lower aqueous percentages (more organic solvents) with some success.
  • Impact on Retention: Using mobile phases with a higher water content in C8 columns can lead to shorter retention times for analytes. Conversely, mobile phases with a lower water content will result in longer retention times. This flexibility allows for fine-tuning of separation based on your needs.
  • Method Development: The broader compatibility of C8 with mobile phases offers more freedom during method development. You can experiment with different water-to-organic solvent ratios to achieve the desired separation and retention times for your analytes.

C18 Columns: A Preference for Organic-Rich Mobile Phases

  • Mobile Phase Preference: C18 columns typically perform best with mobile phases containing a higher proportion of organic solvents. This aligns with their strong hydrophobic nature, allowing for optimal interaction with non-polar analytes.
  • Impact on Retention: Similar to C8, mobile phases with more water in C18 columns will lead to shorter retention times. However, due to the stronger hydrophobicity, even with higher water content, C18 columns might still retain analytes to a greater extent compared to C8.
  • Method Development: When using C18 columns, method development might involve focusing on the selection and optimization of organic solvents within the mobile phase. This helps achieve the desired balance between retention and resolution for your target analytes.

7. Practical Considerations

Now that you’ve delved into the technical aspects of C8 and C8 columns, let’s explore some practical considerations to help you make an informed decision:

Cost and Availability:

  • C18 Columns: Generally more affordable and widely available due to their higher demand.
  • C8 Columns: Might be slightly more expensive due to lower production volume, but still readily available from most chromatography suppliers.

Durability and Lifespan:

  • Both C8 and C18 columns: Offer good durability with proper use and maintenance. Their lifespan depends on factors like the frequency of use, the types of samples analyzed, and the mobile phase conditions.

Ease of Use and Maintenance:

  • C8 and C18 columns: Both are relatively easy to use and maintain. They require following standard HPLC practices for column cleaning and regeneration to ensure optimal performance and longevity.

Choosing the Right Fit:

When making your choice, consider the following:

  • Sample type: For non-polar samples, C18 is the more cost-effective option. For moderately polar samples, C8 might be a good choice, but consider the potential trade-off in retention compared to C18.
  • Budget: If cost is a major concern, C18 might be the more practical option due to its lower price point.
  • Availability: Both columns are widely available, but in rare cases, C8 might have slightly lower stock availability depending on the supplier.


In this blog, we’ve explored the key differences between C8 and C18 HPLC columns, focusing on their chemical composition, retention and separation efficiency, hydrophobicity, sample compatibility, mobile phase considerations, and practical aspects like cost and durability.

  • Chemical Composition: C8 columns have shorter carbon chains (octyl), while C18 columns have longer carbon chains (octadecyl), making them more hydrophobic.
  • Retention and Separation Efficiency: C8 columns provide shorter retention times and are better for polar compounds, while C18 columns offer longer retention times and are ideal for non-polar compounds.
  • Hydrophobicity and Polarity: C8 columns are less hydrophobic, making them suitable for polar compounds, whereas C18 columns are highly hydrophobic, suited for non-polar compounds.
  • Sample Compatibility: C8 columns are versatile for a mix of polar and non-polar compounds, while C18 columns excel with highly hydrophobic samples.
  • Mobile Phase Considerations: C8 columns often require less organic solvent, whereas C18 columns may need more, affecting method development.
  • Practical Considerations: C8 columns are usually more cost-effective, but C18 columns offer greater durability and longer lifespan.

Contact us

If you have any questions or need personalized advice on selecting the right HPLC column for your application, feel free to reach out. You can contact me via email for detailed guidance and support tailored to your specific needs. Let’s ensure you get the best possible results from your HPLC analyses.

Contact us at: sales@uhplcs.com.

About uHPLCs

UHPLCs is a leading manufacturer of HPLC columns and consumables for liquid chromatography. The company offers a wide range of products, including empty HPLC columns, solvent filters, guard columns, inline HPLC columns, and PEEK consumables. uHPLCs’ products are used in a variety of applications, including pharmaceutical, biotechnology, environmental, and food safety analysis.

UHPLCs is committed to providing high-quality products and services to its customers. The company has a strong team of engineers and scientists who are dedicated to developing innovative products and solutions. uHPLCs also has a global network of distributors and sales representatives who can provide support to customers around the world.

If you are looking for a reliable supplier of HPLC columns and consumables, uHPLCs is the perfect choice. The company’s products are of the highest quality and its services are unmatched in the industry.

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