Liquid Chromatography Detectors - Dispersion in Detector Sensors > Dispersion in Connecting Tubes > Page 3

Dispersion in Detector Sensors

There are three sources of dispersion in LC detector sensors,

1. Dispersion from Connecting Tubes(Newtonian)
2. Dispersion from Sensor Cell Volume (Newtonian)
3. Dispersion from Sensor Cell Volume ( Dilution)

Each of these sources of dispersion are controllable by careful sensor design and employing appropriate cell geometry.

Dispersion in Connecting Tubes

The dispersion that takes place in an open tube results from the parabolic velocity profile that occurs under conditions of Newtonian flow, (i.e. when the velocity is significantly below that which produces turbulence). Under condition of Newtonian flow, the distribution of fluid velocity across the tube adopts a parabolic profile as shown in figure 1. The velocity at the walls is virtually zero and that at the center a maximum. This situation is depicted diagramatically in Figure 1.

Figure 1. The Parabolic Velocity Profile of a Solute Band Passing Through a Tube

Due to the relatively high velocity at the center of the tube and the very low velocity at the walls, the center of the band of solute passing down the tube will move ahead of that situated at the walls. The resulting effect of band dispersion is depicted in figure 2.