Introduction

Stainless steel remains the most commonly used material in HPLC column hardware because of its excellent mechanical strength, pressure tolerance, and corrosion resistance. Most chromatography systems and columns utilize either 304 or 316 stainless steel, with 316 stainless steel generally preferred for more demanding analytical applications.

While stainless steel performs exceptionally well in most chromatographic methods, certain analytes can interact with exposed metal surfaces. These interactions may introduce variability, reduce analyte recovery, or affect chromatographic performance, particularly in bioanalytical and LC-MS applications.  To address these challenges, metal-free coated stainless steel hardware has been developed to provide the durability of stainless steel while significantly reducing direct analyte contact with metallic surfaces.

Common Stainless Steel Grades Used in Chromatography

Two stainless steel grades are most frequently encountered in chromatography hardware:  304 Stainless Steel.  Typical composition includes:

• Approximately 18% Chromium
• Approximately 8% Nickel

This material offers good corrosion resistance and is widely used in many industrial and laboratory applications.

316 Stainless Steel

Typical composition includes:

• Approximately 16% Chromium
• Approximately 10% Nickel
• Approximately 2% Molybdenum

The addition of molybdenum improves resistance to:

• Corrosion
• Chloride-containing solutions
• Aggressive mobile phases
• Saline environments

For this reason, 316 stainless steel is often preferred for analytical and biopharmaceutical applications.

Why Corrosion Resistance Matters

Although 316 stainless steel provides superior corrosion resistance compared with 304 stainless stee l, no stainless steel is completely immune to chemical attack.  In chromatography, even extremely low levels of corrosion or surface interaction may affect:

• Sensitive LC-MS methods
• Biologic separations
• Trace-level analyses
• Recovery studies
• Metal-sensitive compounds

Importantly, these interactions may occur at levels too small to be visible during routine inspection.

Analytes That May Be Sensitive to Metal Surfaces

Certain compounds can interact strongly with exposed stainless steel.

Examples include:

• Chelating agents
• Phosphates
• Proteins
• Peptides
• Biomolecules
• Metal-binding compounds
• Certain antifungal agents

Potential consequences include:

• Peak tailing
• Reduced recovery
• Retention shifts
• Method drift
• Quantitative variability

For these applications, reducing contact with metallic surfaces may improve analytical performance.

Metal-Free Coated Stainless Steel Hardware

Metal-free coated hardware utilizes a specialized inert surface treatment applied to the stainless-steel substrate.  This approach helps create a barrier between the analyte and the underlying metal while retaining the mechanical strength of stainless steel.  The result is a hardware platform that provides:

• Excellent durability
• High-pressure capability
• Reduced analyte interaction
• Improved chemical resistance

These features make coated hardware attractive for both traditional HPLC and advanced LC-MS applications.

Advantages Compared to PEEK Hardware

PEEK components are often selected when metal exposure is a concern, but coated stainless steel hardware may offer advantages in certain applications.  Potential benefits include:

• Higher pressure capability
• Greater mechanical strength
• Enhanced durability
• Broader compatibility with demanding chromatographic conditions

This allows chromatographers to maintain the robustness of stainless steel while reducing unwanted metal-related effects.

Key Benefits of Metal-Free Coated TYPE-C™ Hardware

Metal-free coated Cogent TYPE-C™ column hardware and frits can provide advantages such as:

• Improved performance with chelating agents
• Reduced metal interaction during phosphate analysis
• Better recovery of metal-sensitive analytes
• Enhanced protein analysis with reduced adsorption
• Greater durability than many polymer-based alternatives
• Increased suitability for corrosive or chloride-containing environments

These benefits can contribute to more consistent chromatographic performance and improved analytical reliability.

Applications

Metal-free coated hardware is particularly useful for:

• LC-MS methods
• Biopharmaceutical analyses
• Protein separations
• Peptide analyses
• Phosphate determinations
• Chelator analysis
• Trace-level quantitation
• Metal-sensitive compounds

In these applications, minimizing surface interactions can significantly improve method robustness.

Conclusion

Although 316 stainless steel remains one of the most corrosion-resistant materials commonly used in HPLC hardware, certain analytes can still interact with exposed metal surfaces and affect chromatographic performance. Metal-free coated stainless steel frits and hardware provide an effective solution by combining the mechanical strength of stainless steel with an inert surface that helps minimize metal-analyte interactions. For protein analyses, phosphate determinations, chelating agents, and other metal-sensitive applications, coated hardware can improve recovery, reproducibility, and overall method performance.