Preparative Chromatography - Sample Mass Overload > Page 21

Again the retention time of all the peaks are reduced, but not to the same extent as with benzene overload. This is probably due to the distribution coefficient of naphthalene being much larger than benzene and, although the deactivation of the silica gel will be greater, there will be much less solute in the mobile phase to increase the elution rate. This might imply hat that the greater change in retention from benzene over load arises more from the increased polarity of the mobile phase than from the deactivation of the stationary phase.

A sample of more polar solutes (viz. anisole, benzyl acetate and acetophenone) were examined, employing a 5% v/v of diethyl ether in n-heptane as the mobile phase. The reference sample that exhibited no over load contained 19.8 mg of anisole, 44.6 mg of benzyl acetate and 20.5 mg of acetophenone. The sample volume was maintained constant at 200 ml and the mass of benzyl acetate increased from 1.1 to 30 mg in a series of steps. A plot of the retention distances of the front and back inflection points of the elution curve of each solute against the mass of benzyl acetate injected is shown in figure 10. It is seen that the curves are very similar to the shown in figure 9. It is seen that there is little change in the retention of anisole or acetophenone as the load of benzyl acetate increases but the band width of acetophenone is significantly increased.

After J. Chromatogr., Ref. (3)


Figure 10. The Effect of Mass Overload of Benzyl Acetate on the Retention of Anisole, Benzyl Acetate and Acetophenone