Column geometry — What is the principal benefit of decreasing the internal diameter of a chromatographic column (all else equal)?

Introduction / Context:
Changing column internal diameter (ID) profoundly affects chromatographic performance. Narrower columns often deliver higher efficiency and sensitivity but at the cost of load capacity and with increased pressure demands for the same linear velocity.

Given Data / Assumptions:

• Narrower ID reduces radial diffusion paths and can improve mass transfer.
• At matched linear velocity, smaller ID typically increases plate number per time.
• Sample capacity (maximum mass before overload) decreases with column cross-sectional area.
• Pressure requirements rise for smaller IDs at the same linear velocity/particle size.

Concept / Approach:
Identify which listed outcome reliably improves when ID is decreased: resolution commonly increases because efficiency (N) improves and extra-column effects become more manageable with proper instrumentation. Capacity does not increase, and overload risk actually increases for the same mass on a smaller column.

Step-by-Step Solution:

Verification / Alternative check:
Method transfers from 4.6 mm to 2.1 mm ID LC columns often show sharper peaks and better resolution at scaled flows, confirming the principle.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming smaller ID always reduces pressure; it usually does the opposite unless flow is scaled down.

Final Answer:
Increased resolution due to higher efficiency and better mass transfer.