EFFECT OF COLUMN TO PARTICLE DIAMETER RATIO ON DISPERSION OF UNSORBED SOLUTES IN CHROMATOGRAPHY

The dispersion of unsorbed solutes eluted by water through 150-cm columns packed with spherical glass beads has been reexamined using large beads of various sizes and columns of different diameters. It is shown that the dependence of the plate height on velocity, which is similar to that previously found, follows the empirical equation h=(1/2 λ + 1/Cvn)-1 where the reduced plate height h=H/dp, and the reduced fluid velocity v=vdp/Dm. The optimum value of n is 0.3±0.1. Plots of log h vs. log v were coincident for column to particle diameter ratios, p<6 and again for p>8. The latter constancy is in contrast to previous results and it is concluded that the high values of h obtained at high values of p in previous work were due to difficulties in packing the finer particle used. The sharp increase in h by a factor of about 1.8 for the range 6<p<8 is consistent with some results obtained by Sternberg and Poulson for gas phase eluents, but has no obvious explanation. The constancy of h for high values of p can be explained by the application of the Giddings nonequilibrium theory to a model column, possessing a discrete wall layer, in which a serious perturbation of velocity occurs. A hexagonal column showed poorer efficiency than the normal round column and an infinite diameter column showed higher efficiency than normal columns and less dependence of h upon v, the optimum value of n being about 0.2. It is concluded that infinite diameter columns offer some advantages over conventional columns in high pressure, small particle, liquid chromatography. © 1969, American Chemical Society. All rights reserved.