Liquid Chromatography Detectors - Dispersion in Detector Sensors > Low Dispersion Tubing > Page 7

Low Dispersion Tubing

In order to avoid dispersion in mobile phase conduits a number of attempts to design low dispersion tubing has been reported. The first attempt was by Halasz et al. (8), who crimped and bent the tube into different shapes to interrupt the Newtonian flow and introduce radial flow within the tube. His devices had limited success and the tubes had a tendency to block very easily.

In 1978 Tijssen (9), developed a theory to describe the radial flow that was induced into coiled tubes by the continual change in direction of the fluid as it flowed round the spirals (his theory will be considered in detail in Book 9). Tijssen found that by coiling the tubes significantly reduced dispersion, particularly at high flow rates However, the coils were a little clumsy to form as the radius of the coil was required to be less than 3 times the internal radius of the tube for optimum performance. A more practical system was introduced by Katz and Scott (10), who developed a serpentine form of connecting tube that met the requirement that the radius of the serpentine bends (a/2 in the diagram) was less that 3 times that of the internal radius of the tube. A diagram of a serpentine tube is shown in figure 3.

Figure 3 Low Dispersion Tubing

During passage through the tube, the direction of mobile phase flow  changed by 180o as it passed from one serpentine bend to another. This violent change in direction resulted in extensive radial flow which aided radial transfer and greatly reduced the dispersion.