Extra Column Dispersion - Introduction > Page 1

Introduction

Columns with very low plate heights and corresponding high efficiencies can be easily and reproducibly prepared using modern packing techniques (for capillary columns precise coating procedures) in conjunction with well designed stationary phases and supports. Columns having very high efficiencies, however, produce very narrow peaks with very small peak volumes and, thus, the impressive advances in column technology have been accompanied by a continual reduction in peak size. As a consequence, all dispersion processes that takes place outside the column, once relatively unimportant, have now become far more significant and potentially more deleterious to chromatographic performance. Almost all of the dispersion processes that occur outside the column can be minimized by careful design, unfortunately, however, few can be eliminated altogether. Thus, as the techniques have progressed and better performance has been achieved, so has more attention been given to apparatus design as opposed to merely optimizing the distribution system that produces the separation. This also implies that if older chromatographs are employed with modern LC columns (particularly microbore columns) then the expected efficient performance from such columns may not be realized, and, in fact, may not even be attainable.

Sources of Extra Column Dispersion

There are a number major sources of extra column dispersion in any given chromatographic apparatus, and these are depicted diagramatically in figure 1.

Figure 1 Sources of Extra Column Dispersion