One advantage of Controlled-Flow and Zero-Flow capillaries is their specialized inner-wall polymer coating, which significantly reduces sample interaction compared to bare silica capillaries.

As a result, these capillaries typically provide:

• Reduced analyte adsorption
• Improved peak shape
• Better migration reproducibility
• Increased method robustness
• Improved analyte recovery

However, adsorption behavior can still vary depending on the physical and chemical properties of the analyte.

The Impact of Analyte Hydrophobicity

Hydrophobic compounds generally have a greater tendency to interact with polymer-coated surfaces.

As analyte hydrophobicity increases:

• Surface interactions may become more significant
• Recovery may decrease
• Peak response may be reduced
• Migration behavior may be altered

This is especially important when working with neutral hydrophobic molecules.

The Impact of Analyte Charge

Charged analytes typically exhibit minimal adsorption within Controlled-Flow and Zero-Flow capillaries.

Because charge promotes electrophoretic migration and reduces affinity for the polymer coating, these compounds are generally less likely to interact with the capillary wall.

In most cases:

• Positively charged analytes show low adsorption
• Negatively charged analytes show low adsorption
• Charged compounds maintain more predictable migration behavior

Troubleshooting Adsorption-Related Issues

If unexpected results are observed, consider whether analyte adsorption may be contributing to:

• Reduced sensitivity
• Lower recovery
• Delayed migration
• Peak distortion
• Reproducibility issues

Evaluating the analyte's charge state and hydrophobicity is often the first step in determining whether wall interactions are affecting performance.