Visualization of sample introduction in liquid chromatographic columns. Contribution of a flow distributor on the...

The contributions to the radial distribution of the sample concentration across the column inlet and to the axial band dispersion resulting from a column header containing a distributor were evaluated using a band-visualization process entailing matching the refractive indices of the stationary and mobile phases in a glass column. This study illustrates graphically how a distributor fitted to the column can increase the axial dispersion of the sample band compared to an inlet containing only a frit. The distributor did not provide a uniform sample distribution across the column. In fact, for 17-mm inner diameter columns and high-porosity frits, the distribution was no better than with the frit having no distributor. However, when low-porosity frits were employed, improved peak shapes were obtained with a distributor. In addition, we observed that the inlet header configuration influenced dramatically the flow stream established along the column. The radial distribution of the efficiency of the columns was nearly homogeneous for those having only a frit but not for those having also a distributor. For the latter, the efficiency decreased from the column axis to its wall.