Each ion had to be determined one at a time separately from all other ions present and sample preparation time was long, often involving lengthy protocols, which required the use of potentially hazardous analytical reagents. However, within the past ten years or so, commercial instruments have become available which greatly reduce the sample preparation time and which allow simultaneous determination of all anions of interest in a sample during a single pass. This instrumental method is called Ion Chromatography. There are many different kinds of chromatography, among them paper chromatography, gas chromatography, liquid chromatography, and ion-exchange chromatography. An ion chromatograph is an example of the latter kind of chromatography.
All chromatographic methods share the same basic principles and mode of operation.
The compounds contained in the analyte are then partitioned between the stationary adsorbent and the moving eluent. The success of the method depends on the fact that different materials adhere to the adsorbent with different forces. Some adhere to the adsorbent more strongly than others and are therefore moved through the adsorbent more slowly as the eluent flows over them. Other components of the analyte are less strongly adsorbed on the stationary phase and are moved along more quickly by the moving eluent. So, as the eluent flows through the column, the components of the analyte will move down the column at different speeds and therefore separate from one another, as shown in the diagram below.