HPLC Fittings and Tubing: PEEK vs Stainless Steel (Which to Use)

Use stainless steel tubing for UHPLC and high-pressure methods (above roughly 5,000 psi / 350 bar) or when your mobile phase contains THF, DMSO, or chlorinated solvents. Use PEEK tubing for metal-sensitive samples, high-chloride buffers, and moderate-pressure routine HPLC where easy finger-tight installation matters.

What Are HPLC Fittings and Tubing?

HPLC tubing carries the mobile phase and sample between the pump, autosampler, column, and detector. Fittings (nuts and ferrules) connect that tubing to each port and create a leak-free seal. Together, they form the flow path, and their material, inner diameter (ID), and connection quality directly affect pressure, peak shape, and reproducibility.

What Is the Difference Between PEEK and Stainless Steel HPLC Tubing?

PEEK (polyether ether ketone) is a chemically resistant, metal-free polymer. Stainless steel is a rigid, high-pressure metal. The main differences are pressure rating, chemical compatibility, metal interaction and installation.

When Should You Use PEEK Tubing?

Choose PEEK when:

• Your analytes interact with metal ions (phosphorylated compounds, chelators, many peptides and proteins)
• You use high-chloride or extreme-pH buffers that can corrode stainless steel
• Your system runs at moderate pressure
• You change columns often and want fast, tool-free connections

When Should You Use Stainless Steel Tubing?

Choose stainless steel when:

• Your method runs above ~5,000 psi, as in most UHPLC work
• Your mobile phase includes THF, DMSO, or methylene chloride
• You need rigid, dimensionally stable connections with minimal dead volume
• Long-term durability matters more than installation speed

Which Tubing Inner Diameter Should You Choose?

Narrower tubing reduces extra-column band broadening but raises backpressure and clogs more easily. Internal volume per 10 cm of tubing:

Rule of thumb: use the narrowest ID your system pressure allows, and keep the tubing between column and detector as short as practical.

What Are the Most Common HPLC Fitting Mistakes?

1. Ferrule not fully seated. The gap creates dead volume, causing peak broadening and tailing.
2. Reusing a swaged ferrule in a different port. Port depths vary, so replace the ferrule.
3. Poor tubing cut. Scissors or knives leave a crushed, angled end. Use a proper tubing cutter and inspect the cut.
4. Over-tightening PEEK fittings. Finger-tight is usually enough. Excess force deforms the tubing.
5. Wrong material for the solvent. Check PEEK compatibility before running THF-containing methods.

How Do You Know When to Replace HPLC Tubing and Fittings?

Replace them when you see:

• Leaks or salt crystals around connections
• Unexplained pressure fluctuations
• New peak tailing or broadening after a column change
• Discoloured, kinked, or swollen tubing

Quick Decision Guide

Frequently Asked Questions

Is PEEK tubing good for HPLC?

Yes, for moderate-pressure methods. PEEK is metal-free, corrosion-resistant, and easy to install, but it is not suitable for UHPLC pressures or solvents such as THF, DMSO, and methylene chloride.

What pressure can PEEK HPLC tubing handle?

Standard PEEK tubing is typically rated to about 5,000 psi (350 bar), varying with inner diameter. Always check the manufacturer’s rating.

Can PEEK tubing be used with THF?

Generally no. THF can swell and weaken PEEK. Use stainless steel for THF-containing mobile phases.

Why does stainless steel cause peak tailing for some samples?

Some analytes, such as phosphorylated and chelating compounds, adsorb onto metal surfaces in the flow path, which leads to tailing, low recovery, or poor reproducibility. A metal-free flow path often fixes this.