Two ion chromatography methods are well known: the suppressed method and the non-suppressed method. The suppressed method is suitable for anion analysis. Sodium carbonate aqueous solution is used as the eluent of Shodex columns for the suppressed method. The suppressor removes sodium ions in the eluent and changes sodium carbonate to carbonic acid with lower conductivity, allowing the background levels to decrease. In addition, the suppressor changes sodium ions (cations), to hydrogen ions with higher conductivity. Therefore the peak response increases and highly sensitive analysis of anions is possible.

Merit of suppressed method.
1. Background conductivity is low.
(anion analysis: about 20 μS/cmFS)
2. Sensitivity is high. Detection sensitivity is several ppb and minimum sample concentration is about tens ppb.
3. Free from temperature fluctuation and stable analysis is possible.

Demerit of suppressed method.
The use of a suppressor is essential and the system is rather expensive.