Service life of counter-current chromatography coils

Area of Science:

• Analytical Chemistry
• Materials Science

Background:

• Centrifugal partition chromatography (CPC) utilizes coils for separation.
• Polytetrafluoroethylene (PTFE) tubing is commonly used for these coils.
• Long-term use of PTFE coils in centrifuges can lead to material failure.

Purpose of the Study:

• To investigate the failure mechanisms of PTFE tubing used in a type J centrifuge.
• To identify the types of defects and their causes in used PTFE coils.
• To suggest alternative materials for improved coil stability in continuous centrifugation.

Main Methods:

• Examination of a multilayer PTFE coil after approximately 3 years of daily use in a centrifuge.
• Identification and characterization of physical defects in the tubing.
• Analysis of PTFE tubing properties, including permeability and expansion in organic solvents.

Main Results:

• Two primary defect types were identified: crazes and indentations.
• Crazes, occurring throughout the coil, can lead to slits, while indentations form on inner layers and cause leaks.
• PTFE tubing showed significant expansion (over 1%) in solvents like hexane and chloroform, and is permeable to air and hexane.

Conclusions:

• PTFE coil defects are attributed to centripetal forces acting on flexible tubing, exacerbated by solvent absorption.
• Indentations likely result from excess tubing length caused by solvent expansion being moved towards the coil center.
• Fluorinated ethylene propylene (FEP) tubing, particularly when etched, is proposed as a more stable alternative due to its lower solvent-induced expansion.