High-performance liquid chromatography (HPLC) systems rely on a range of components, from tubing and fittings to valves and columns, to ensure accurate, reliable separations.
Among the critical decisions in system setup and maintenance is the choice of materials for these components. Two of the most commonly used materials in HPLC systems are stainless steel and PEEK .
Each has unique properties that make it more or less suitable depending on the application, sample type, and operational requirements. This article explores the advantages, limitations, and best use cases of stainless steel and PEEK components to help users make informed choices for their HPLC setups.
Material Overview: Stainless Steel vs. PEEK
Stainless Steel
Stainless steel, typically grade 316 or 316L, is a corrosion-resistant alloy widely used in HPLC components such as tubing, fittings, columns, and valves. Its key attributes include:
●High mechanical strength: Can withstand very high pressures typical in HPLC operations (up to 6000 psi and above).
●Excellent chemical resistance: Stable with most solvents used in reversed-phase and normal-phase chromatography, except strong acids or halogenated solvents in some cases.
●Thermal stability: Maintains integrity at elevated temperatures, useful for column ovens or high-temperature applications.
●Minimal interaction: Generally inert to many analytes, reducing sample adsorption risks.
PEEK
PEEK is a high-performance thermoplastic polymer increasingly used in HPLC system components. Key features include:
●Chemical inertness: Resistant to a wide range of solvents, acids, bases, and biological samples, making it ideal for sensitive or reactive analytes.
●Low surface adsorption: Less likely to interact with polar or ionic compounds, reducing sample loss or degradation.
●Flexibility and lightweight: Easier to handle and install compared to rigid stainless steel.
●Lower cost: Generally less expensive than stainless steel, especially for tubing and fittings.
However, PEEK has lower mechanical strength and temperature resistance than stainless steel, typically rated for pressures up to around 6000 psi (but often recommended for lower to moderate pressures) and maximum temperatures around 60–80°C.
Comparing Performance in HPLC Systems
1.Pressure and Mechanical Strength
●Stainless steel’s superior mechanical properties make it the material of choice for high-pressure applications such as UHPLC, where system pressures can exceed 15,000 psi. Stainless steel tubing and fittings provide robust performance and durability under these conditions.
●PEEK components, while pressure-rated for typical HPLC conditions (up to ~6000 psi), may not be suitable for UHPLC or applications with frequent pressure spikes. Overpressurization can cause PEEK tubing to deform or fittings to leak.
2.Chemical Compatibility
●PEEK shines when handling aggressive or sensitive samples. For example, it is preferred in bioanalytical applications involving proteins, peptides, or samples prone to metal-catalyzed degradation or adsorption. Stainless steel can sometimes interact with metal-sensitive analytes, causing peak tailing or sample loss.
●However, stainless steel outperforms PEEK when exposed to strong acids (like hydrochloric acid) or halogenated solvents, which can degrade or swell PEEK components over time.
3.Temperature Resistance
●Stainless steel maintains structural integrity well beyond 100°C, suitable for applications requiring column heating.
●PEEK typically has a maximum continuous use temperature around 80°C, limiting its use in heated environments.
4.Sample Adsorption and Inertness
●PEEK’s polymeric surface reduces interaction with polar, ionic, or bio-molecules, minimizing sample adsorption and improving peak shape and reproducibility for these analytes.
●Stainless steel surfaces, while generally inert, can sometimes cause adsorption or catalytic effects, especially with sensitive samples or at elevated temperatures.
5.Cost and Ease of Use
●PEEK components are usually less expensive and easier to cut and install, thanks to their flexibility. This makes them popular for routine maintenance and when frequent system changes are needed.
●Stainless steel requires special tools and expertise to cut and properly install, increasing labor and maintenance costs but rewarding with longevity.
When to Choose Stainless Steel vs. PEEK Components in HPLC Systems
| Criteria | Stainless Steel | PEEK |
| Pressure Requirement | Suitable for high or ultra-high pressures (e.g., UHPLC) | Suitable for moderate pressures (<6000 psi) |
| Temperature Conditions | Ideal for high-temperature operations | Best for ambient temperature conditions |
| Solvent Compatibility | Excellent for aggressive solvents (strong acids, halogenated solvents) | Suitable for aqueous or mildly acidic/basic solvents |
| Sample Sensitivity | Use when sample is not sensitive to metal surfaces | Use for bio/pharma samples or trace metals |
| Durability | Long-lasting and robust | Easier to damage under extreme conditions |
| Ease of Replacement | More effort required for replacement | Easy and quick to replace |
| Metal Contamination Concern | Not suitable when metal contamination must be avoided | Preferred for trace metal analysis |
| Cost | Higher initial cost, but long-term value | Lower cost, convenient for temporary setups |
Hybrid Approaches: Combining Stainless Steel and PEEK
Many modern HPLC systems use a combination of stainless steel and PEEK components to leverage the strengths of both materials.
For example:
Stainless steel tubing and fittings in high-pressure sections near the pump and column.
PEEK tubing and connectors in low-pressure or sample introduction sections.
PEEK-lined stainless steel columns combining durability with inert sample paths.
This hybrid approach balances cost, performance, and sample integrity.
Maintenance Tips for Both Materials
For stainless steel: Regularly inspect for corrosion or scratches that could trap samples. Clean with appropriate solvents to avoid buildup.
For PEEK: Avoid exposure to strong acids, elevated temperatures, and mechanical stress to prevent deformation or cracking. Replace tubing regularly in critical applications.
Fittings and seals: Ensure proper torque settings and use compatible ferrules to avoid leaks.
Conclusion
Choosing between stainless steel and PEEK components in HPLC systems depends largely on the application requirements, sample nature, and operational parameters.
Stainless steel offers superior mechanical strength, pressure tolerance, and temperature stability, making it ideal for demanding and high-pressure applications. PEEK, with its chemical inertness and low adsorption, is well suited for sensitive samples and moderate operating conditions.
Understanding the strengths and limitations of each material enables chromatographers to build HPLC systems that optimize performance, durability, and data quality.
Still not sure whether stainless steel or PEEK is right for your system?
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