Liquid Chromatography Detectors - Dispersion in Detector Sensors > Low Dispersion Tubing > Page 9

Despite the apparent advantages, low dispersion serpentine tubing appears to have been employed in only one commercial LC detector. It should be pointed out that any conduit system that has low dispersion will also provide very fast heat transfer rates. Serpentine tubing has been also used in commercial column ovens to heat the mobile phase rapidly to the column oven temperature before it enters the column. The serpentine tubing allows effective heat exchange with a minimum of heat exchanger volume to distort the concentration profile of the solvent gradient.

The different forms of dispersion profiles that are obtained from various types of connecting tubes used in LC are shown in figure 4.

Figure 4 Dispersion Profiles from Different Types of Tube

 

These dispersion curves were obtained using a low dispersion UV detector (cell volume, 1.4 ml) and a sample valve with a 1 ml internal loop. All tubes were of the same length and carried the same mobile phase at a flow rate of 2 ml/min. employed. The peaks were recorded on a high speed recorder. The peak from the serpentine tubing is seen to be symmetrical and has the smallest width. The peak from the coiled tube, although still very symmetrical is the widest at the points of inflexion of all four peaks. The peak from the straight tube 0.25 mm I.D. is grossly asymmetrical and has an extremely wide base width. The width and asymmetry is reduced using a tube with an I.D. of 0.18 mm but serious asymmetry remains. Where the design of the chromatograph precludes a close proximity between the column and the detector, the use of low dispersion serpentine tubing may be a satisfactory alternative.