Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > Page 11

 

Figure  3. Graph of Column Length Traveled by the Solute Before Radial Equilibrium is Achieved against Particle Diameter

 Despite the lack of radial equilibrium, however, if the column packing is completely homogeneous throughout the column length, then the column efficiency should not be impaired. Unfortunately, ideal packing conditions are not always achieved and channeling often occurs, under which circumstances lack of radial equilibrium could result in the column efficiency being reduced with consequent loss in resolution. To ensure radial equilibrium, it must either be achieved on injection (using sample distribution device) or by employing narrow bore columns where radial equilibrium is more quickly reached. The latter alternative, however, will depend on the resolution required and the nature of the sample.

Dispersion Processes that take Place in an LC Column

There are four basic dispersion processes that can occur in a packed column that will account for the final band variance. They are, Multipath dispersion, dispersion from Longitudinal Diffusion, dispersion from the Resistance to Mass Transfer in the Mobile Phase and dispersion from the Resistance to Mass Transfer in the Stationary Phase. All these processes are random and essentially non-interacting and, therefore, provide individual contributions of variance that can be summed to produce  the final band variance.