The column dimensions will also depend on the type of separation that is envisaged. The choice of column diameter will depend on the capacity of the ion exchange media and also the scale of the separation. Columns packed with low capacity ion exchange material, or those that are are to be used for preparative purposes, will require large diameter columns (up to 5 cm in diameter and under special circumstances even more). Columns required for high resolution separations will need to be fairly long to provide the necessary large number of theoretical plates and will be perhaps 3mm in diameter.
Columns used for fast analysis are usually short (3cm-5 cm long) and (3mm to 4.6 mm) in diameter. In general, the faster the column the shorter it will need to be and the lower the resolution. In contrast, the greater the resolution that is required, the longer the column will be and the smaller the diameter. An example of a commercial analytical column having medium resolution and speed is shown in figure 19.
Figure 19. A General Purpose Ion Exchange Column
Ion chromatography, by definition, separates substances that ionize and as the electrical conductivity detector can only detect those substances that produce ions, it is this detector that is used extensively in ion chromatography. A.J.P. Martin invented the electrical conductivity detector in 1944.
Other detectors such as the UV detector, and in certain instances the fluorescence detector can also be employed but without doubt, the electrical conductivity detector is by far the most popular. As a consequence, only the electrical conductivity detector and the UV detector will be described in detail.