Extra Column Dispersion - Low Dispersion Connecting Tubes > Serpentine Tubes > Page 34
Low dispersion tubing has a another feature that follows directly from its operating principle. The secondary flow that results from its serpentine form greatly increases its thermal conducting properties. It follows that serpentine tubes are also highly efficient heat exchangers. Serpentine tubing has been used to preheat the mobile phase before entering a thermostatted column. A few centimeters of serpentine tubing were found to be sufficient to achieve complete thermal equilibrium between the column and the mobile phase.
The different forms of dispersion profiles that are obtained from various types of connecting tubes used in LC are shown in figure 14. The peaks shown were obtained using a low dispersion UV detector (cell volume, 1.4 ml) in conjunction with a sample valve witha 1 mlinternal loop. The tubes had the same length and the flow rate was 2 ml/min.; the peaks were recorded on a high speed recorder. The serpentine tubing is seen to produce symmetrical peaks which had the smallest width. The peak from the coiled tube, albeit quite symmetrical, is the widest of all four peaks at the points of inflexion.
Ref (P) J. Chromatogr. 268(1978)681
Figure 14. Dispersion Profiles from Different Types of Tube