For chosing the right eluent the kind of separated sample ions as well as the type of separation column is important.
The most common eluents for ion chromatography are based on hydroxide or carbonate as aluting anion.
Carbonate eluents
Carbonate eluents are used in anion analysis. The eluent is an aqueous solution of carbonate and hydrogen carbonate salts. It has the advantage that the total ion strength as well as the compounding of HCO3- and CO32- ions can be varied to change the retention time and the selectivity between monovalent and multivalent sample ions.
Hydroxide eluents
Hydroxide eluents should be prepared from sodium hydroxide or potassium hydroxide. The advantage of using hydroxide eluent is that it is transformed into pure water in the supressor and so gives a very low background conductivity.