Ion exchange columns vary widely in size, packing material and material of construction. Depending on its ultimate use and area of application the column material may be stainless steel, titanium, glass or an inert plastic such as PEEK. The column can vary in diameter from about 2mm to 5 cm and in length from 3 cm to 50 cm depending on whether it is to be used for normal analytical purposes, microanalysis, high speed analyses or preparative work.
Figure 18. Different Forms of Ion Exchanger Media
The packing material can also vary in form from bonded irregular silica, to pellicular packing, macroporous or microporous cross-linked polystyrene and hydrophilic methylmethacrylate beads. Micrographs of some of the different types of packing are shown in figure 18, Much mystique has been woven around the procedure of column packing. The vast majority of LC columns are slurry packed and in practice, it is a relatively simple operation but, without the appropriate equipment, it can be a long and tedious procedure. Today (despite the high cost involved) the majority of columns are purchased, packed with the material selected for the intended application. Columns are available commercially, for general-purpose work or can be designed for specific analyses. Most columns are supplied to defined specifications, which can be evaluated by the analyst and are usually accompanied with cleaning instructions, All columns will deteriorate with time but this is often due to sample contamination. In many cases the column can be cleaned by the recommended procedure provided with the column and brought back close to its original level of performance. However, a column will eventually deteriorate to an unacceptable level that can not be recovered by cleaning and then must be replaced. The life of a column will depend largely on the type of samples it is used to separate but the conditions under which the separations are carried out will also place limits on it useful lifetime