Q1(b). Particle diameter in chromatography

Answer in brief

Smaller uniform particles improve efficiency, but require higher pressure.

Key points

• The plate height is represented by H=A+B/u+Cu. Smaller packing particles reduce multiple-path dispersion, the A term, and shorten mass-transfer distances, reducing C.
• Consequently H falls and the number of plates N=L/H rises for a fixed column length, producing narrower peaks and improved resolution.
• Smaller particles can permit faster operation without a large efficiency loss. A narrow particle-size distribution and good packing are also important.
• Pressure drop approximately varies as ΔP∝ Lu/dₚ². Very small particles therefore demand pressure-rated equipment and good filtration; choose size to balance resolution, time and pressure.