Which statement best describes the van Deemter plot in chromatography?

Which statement best describes the van Deemter plot in chromatography?

• A. The relationship between temperature and plate height.
• B. The relationship between velocity and plate height in chromatography.
• C. The relationship between pressure and viscosity.
• D. The relationship between concentration and diffusion.

Answer: (B)

The van Deemter plot shows how the efficiency of a chromatographic column, quantified by the plate height H, changes as you vary the mobile-phase linear velocity. The relationship is described by H = A + B/u + C u, where A is eddy diffusion from multiple flow paths, B/u accounts for longitudinal diffusion (which dominates at low flow rates), and C u represents mass-transfer resistance between the stationary and mobile phases (which grows with higher flow rates). Because these terms compete, the plot typically has a U-shaped curve: at very low velocities, diffusion broadens bands and increasing H; at very high velocities, rapid movement prevents complete equilibration, also increasing H. There is an optimal velocity where H is minimum, giving the best efficiency and the highest plate number N = L/H. This is why the statement describing the relationship between velocity and plate height in chromatography is the best choice.

The van Deemter plot shows how the efficiency of a chromatographic column, quantified by the plate height H, changes as you vary the mobile-phase linear velocity. The relationship is described by H = A + B/u + C u, where A is eddy diffusion from multiple flow paths, B/u accounts for longitudinal diffusion (which dominates at low flow rates), and C u represents mass-transfer resistance between the stationary and mobile phases (which grows with higher flow rates). Because these terms compete, the plot typically has a U-shaped curve: at very low velocities, diffusion broadens bands and increasing H; at very high velocities, rapid movement prevents complete equilibration, also increasing H. There is an optimal velocity where H is minimum, giving the best efficiency and the highest plate number N = L/H. This is why the statement describing the relationship between velocity and plate height in chromatography is the best choice.