It is interesting to note from equation (60) that when a capillary column is run at its optimum velocity, the maximum efficiency attainable is directly proportional to the inlet pressure and the square of the radius and inversely proportional to the solvent viscosity and the diffusivity of the solute  in the mobile phase. This means that the maximum efficiency attainable from a capillary column increases with the column radius. Consequently, very high efficiencies will be obtained from relatively large  diameter, but very long, columns.

Employing equation (60) it is possible to calculate the range of efficiencies attainable under operating conditions commonly used for packed columns. The conditions assumed are as follows,

                Inlet Pressure  1000 lb/sq.in.

                Viscosity of Mobile Phase 0.00397 Poises

                Diffusivity of the Solute in the Mobile Phase 2.5 X 10^-5

                     cm²/sec

The results obtained are shown as a graph relating column efficiency against column radius in figure 18.

Figure 18. Graph of Log. Efficiency against Log, Radius for an LC Capillary Column Operated at its Optimum Velocity.