Dispersion in Chromatography Columns - Resistance to Mass Transfer Dispersion > Diffusion Controlled Dispersion in the Mobile Phase > Page 33


and thus, for a capillary column,


                     .                 (19)

The argument used to develop the function describing (tm) for a capillary column is similar to that for the packed column but (r), the column radius, replaces (dp) the particle diameter.

Due to the varying physical nature of the different packings, it appears column, but it was suggested by Klinkenberg and Purnell that as no one has developed a specific function for () for a packed columns,

that the function,    

(developed by Golay for the capillary column) could also be used for packed GC and LC columns.  However, in a packed column. the flow patterns in interstices between the particles is very complex and the eddies and pseudo turbulence that are generated between the particles greatly increases the effective diffusivity of the solute in the mobile phase. In fact, the magnitude of equation (18) can be so reduced by the large increase in (Dm) that the overall contribution to the peak dispersion can become small enough to be ignored.