Column

The column is a fundamental part of the HPLC system since it is where the separation of the analytes takes place. The column is packed with small beads made of silica that can be coated. It is the surface material covering the beads that determine the polarity. Silica beads are polar in their nature, but when coated with long carbon chains, they become non polar. Because the beads inside the column are stationary during the run, they are also referred to as the stationary phase.

In reverse phase, the stationary phase packed in the column is non polar. Therefore, non polar analytes will interact with the column and stay longer there, leaving the column later than polar compounds.

Figure 1. This image illustrate the beads that are densely packed inside a column, as shown by the first circular inlet. When we zoom in to the individual beads, as shown by the second circular inlet, you can see the material coating the beads surface.

Figure 2.Polarity scale for stationary phase.