Overview

PEEK (PolyEtherEtherKetone) is widely used in chromatography systems for fittings, tubing, and in-line filters due to its strength, flexibility, and broad chemical resistance. However, despite its robust performance in most HPLC applications, PEEK can be chemically attacked or structurally weakened by certain solvents and aggressive reagents.

Avoiding these chemicals helps prevent swelling, embrittlement, discoloration, or failure of PEEK components.

Solvents and Reagents Incompatible With PEEK

The following substances should not be used with PEEK tubing, fittings, or filters, as they can damage the polymer or severely weaken its mechanical integrity:

Strong Mineral Acids

• Nitric acid
• Sulfuric acid

These oxidizing and highly reactive acids can break down PEEK polymer chains and are strictly incompatible.

Halogenated Acids

• Hydrofluoric acid (HF)
• Hydrobromic acid (HBr)
• Hydroiodic acid (HI)

These acids aggressively attack PEEK, causing rapid chemical degradation.

Halogenated Gases

• Pure halogenated gases should not contact PEEK due to their strong reactivity and ability to penetrate and compromise the polymer structure.

Problematic Organic Solvents

• Methylene chloride
• THF (Tetrahydrofuran)
• DMSO (Dimethyl sulfoxide)

These solvents can cause swelling, softening, or dissolution of PEEK over time, especially under pressure or elevated temperatures.

Compatible Solvents and Buffers

Despite the list of incompatible reagents, PEEK is safe for use with many common laboratory solvents and additives:

Generally Compatible

• Hydrochloric acid (dilute)
• Standard HPLC‑grade organic solvents
• Most aqueous buffers used in HPLC

These materials do not typically interact with PEEK in a way that would compromise performance.

Practical Guidance

When to Avoid PEEK

• Use metal or fluoropolymer alternatives if your mobile phase contains halogenated acids or aggressive solvents.
• Avoid PEEK in high‑temperature applications involving solvents known to cause swelling.
• Do not use PEEK for LCMS workflows involving halogen‑rich mobile phases where polymer degradation could introduce background ions.

General Recommendations

• Always verify solvent compatibility when introducing a new reagent into a system containing PEEK components.
• Replace PEEK tubing or fittings immediately if discoloration, softness, cracking, or unexpected pressure changes occur.