The Single Column System

In general an isotachophoretic separation is carried out in a PTFE tube 0.2 to 0.4 mm internal diameter. In most instruments the system is fitted with both conductivity and UV absorption detection. A typical example of an isotachophoretic instrument is shown in figure 14.

Figure 14. Basic Isotachophoretic Apparatus

The apparatus consists of two electrode compartments carrying the leading and terminating electrolytes respectively in which are inserted the anode and cathode, which in turn, are connected to a constant current power supply. A PTFE tube, with inside and outside diameters of 0.2 and 0.3 mm respectively, has been found to be optimum for this type of separation. Tubes of these dimensions have very small convective contributions and minimal temperature affects. The sample is introduced by injection into the sample block.  As the zones are formed each one will assume its own physical characteristics such as temperature, conductance, pH, and potential gradient. In addition some zones may exhibit other characteristics such as radioactivity, UV absorption optical rotation, and fluorescence all of which, using appropriated detecting systems can aid in sample identification. One of the first detection methods was thermal measurement employing very thin constantan/copper thermocouples and although the signal is small it is one of the more sensitive detection devices. Potential gradient detection and conductivity detection is carried out using 25-micron diameter electrodes. The electrodes are cemented into the detector block and the sensor volume is a few nanolitres. The UV sources is normally a low pressure mercury vapour lamp and light is guided by an optical quality glass rod through the separation tube and then by another optical glass rod system onto a suitable photoelectric cell. The different parts of the apparatus are labelled in figure 14.