Carbonate ion is contained in almost all aqueous samples and plays an important role for the ion balance. Therefore, simultaneous analysis of seven common anions (F^-,Cl^-, NO₂^-, Br^-, NO₃^-,HPO₄^2-, SO₄^2-) together with carbonate ion can be considered as an important target for development. Previously there have been examples of analysis including a suppressed IC method using NaOH eluent and a non-suppressed IC method using, a polymethacrylate column, but they were not satisfactory enough in peak shape, peak separation and detection sensitivity. The present method uses IC SI-90 4E and allows the baseline separation of seven common anions together with carbonate ion by non-suppressed IC using the eluent, p-hydroxybenzoic acid, pH 8.2.

(Pretreatment with the cartridges packing Na⁺ type cation exchange resin)
1. Rinse the cartridge with 3 mL of methanol and 3 mL of H₂O separately.
2. Load 3 mL of the sample onto the cartridge.
3. Waste 1 mL of the first elution.
4. Collect 2 mL of following elution.

Sample : 100 μL each
Anion standards solution
1. F^- 2 mg/L
2. HCO₃^- 20 mg/L
3. Cl^- 3 mg/L
4. NO₂^- 5 mg/L
5. Br^- 10 mg/L
6. NO₃^- 10 mg/L
7. HPO₄^2- 15 mg/L
8. SO₄^2- 15 mg/L

River water

Column       : Shodex IC SI-90 4E (4.0 mm I.D. x 250 mm)
Eluent       : 5 mM p-Hydroxybenzoic acid + 5.3 mM N,N-Diethylethanolamine aq.
Flow rate    : 1.5 mL/min
Detector     : Non-suppressed conductivity
Column temp. : 25 °C