Samples containing more than 10 mg/L of Mg²⁺ and/or 20 mg/L of Ca²⁺ must be pretreated, because those divalent cations form complexes with the eluent and give rise to broad peaks which interfere with the analysis. For pretreatment, samples are passed through a pretreatment cartridge packed Na⁺ type cation exchange resin. This replaces the divalent cations in samples by Na⁺ and removes the interfering peaks.

(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 : Mineral water, 100 μL
1. HCO₃^-
2. Cl^-
3. NO₃^-
4. SO₄^2-

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