When working with Trifluoroacetic Acid (TFA) in HPLC, it is important to understand how strong acids interact with polymer-based fittings such as Delrin® (acetal).

While Delrin fittings offer convenience and chemical resistance for many routine HPLC applications, TFA can create conditions where long-term exposure may compromise fitting performance.

Chemical Compatibility Considerations

Interaction Between TFA and Delrin

• TFA is a strong organic acid commonly used in mobile phases for improved peak shape, especially for peptides and proteins.
• Delrin (acetal) is generally resistant to many organic solvents but is not ideal for long-term exposure to aggressive acids such as TFA.
• Extended acid contact can lead to surface weakening, swelling, or slow degradation of Delrin fittings, depending on concentration and system temperature.

Operational Risks

Potential Performance Issues

• Acid interaction may cause the fitting material to soften or lose dimensional stability over time.
• Loss of structural integrity can result in leaks, particularly at high-pressure junctions.
• Temperature, acid strength, and flow duration all influence the degree of impact.

Practical Recommendations

Best Practices When Using TFA

• Consider using PEEK or stainless‑steel fittings in any location where TFA exposure is continuous or where system pressure is high.
• For systems using Delrin fittings, minimize prolonged or repeated direct exposure to strong acids.
• Monitor fittings periodically for visible wear or changes in mechanical behavior.

Choosing the Right Fitting Material

When Delrin May Still Be Acceptable

• Short-term, low-concentration TFA exposure may not cause immediate issues in non‑critical connections.
• Fittings located upstream of the pump or in low-pressure regions generally face less risk.

Recommended Alternatives for Reliability

• PEEK fittings provide excellent chemical resistance and are widely preferred for acidic mobile phases.
• Stainless‑steel fittings are the most durable option for high-pressure and high-acid environments.