Overview

Zero-Flow™ CE capillaries utilize a specialized internal treatment that contributes to their distinctive electroosmotic flow characteristics and separation performance. When preparing a detection window, it is important to remove only the outer polyimide coating while avoiding damage to the internal capillary surface.

Traditional capillary window-making techniques that are commonly used with standard fused silica capillaries may not be appropriate for Zero-Flow™ capillaries because they can damage the internal treatment layer and negatively affect analytical performance.

Why Internal Surface Protection Matters

The internal surface treatment of a Zero-Flow™ capillary plays a critical role in its performance.

Damage to this treated surface may result in:

• Changes in electroosmotic flow behavior
• Reduced separation performance
• Migration time variability
• Peak distortion
• Reduced reproducibility
• Permanent capillary damage

For this reason, methods that expose the capillary to excessive heat should be avoided whenever possible.

Methods That Are Not Recommended

The use of a Window Maker™ device or direct flame exposure is generally not recommended for creating detection windows on Zero-Flow™ capillaries.

Excessive heat may:

• Damage the internal coating
• Create localized coating defects
• Alter capillary performance
• Produce inconsistent analytical results

Although standard capillaries may tolerate these approaches, Zero-Flow™ capillaries require a more controlled method.

Recommended Polyimide Removal Method

The preferred approach for removing the outer polyimide coating is chemical removal using highly concentrated sulfuric acid.

This method dissolves the outer polyimide layer while minimizing the risk of damage to the internal capillary treatment when performed properly.

Users should follow approved laboratory procedures and safety protocols when handling corrosive chemicals.

Alternative Removal Techniques

Carefully controlled low-temperature heating may be used in certain situations to remove the outer coating.

If heat is used:

• Exposure should be minimized.
• Heating duration should be kept as short as possible.
• Excessive temperatures should be avoided.
• The internal capillary surface must be protected.

Because of the potential for damage, chemical removal is generally preferred.

Safety Considerations

Polyimide removal procedures may involve hazardous materials or elevated temperatures.

Appropriate precautions include:

• Proper eye protection
• Chemical-resistant gloves
• Laboratory protective clothing
• Adequate ventilation
• Approved chemical handling procedures
• Proper waste disposal practices

All laboratory safety policies should be followed before beginning any coating removal procedure.

Applications

Proper window preparation is important for:

• UV detection
• CE method development
• Capillary replacement
• Capillary maintenance
• Electrophoresis troubleshooting

Maintaining the integrity of the internal treatment helps preserve the intended performance characteristics of the capillary.

Key Takeaways

• Zero-Flow™ capillaries contain a specialized internal treatment that must be protected.
• Traditional window-making methods may damage the internal capillary surface.
• Chemical removal of the outer polyimide coating is generally preferred.
• Excessive heat can negatively affect capillary performance.
• Careful window preparation helps maintain reproducibility and separation quality.
• Proper laboratory safety procedures are essential during coating removal.

Additional Resources

For capillary dimensions, coating options, migration control technologies, and electrophoresis application guidance, view:  Zero-Flow™ and Controlled-Flow™ CE Capillary Specifications and Selection Guide