Analytical Method: Analytical Quality Assurance, Standard for Free Chlorine (DIN)

Reagents:
Potassium iodate volumetric standard (Product No. 102404)
Potassium iodide (Product No. 105043) for analysis
Sulfuric acid (Product No. 109072 ) 0.5 mol/L
Sodium hydroxide solution (Product No. 109136) 2 mol/L
Water (Product No. 116754) for analysis

Preparation of a KlO₃ stock solution:
Dissolve 1.006 g of KlO₃ in 250 mL of water for analysis in a calibrated or conformity-checked 1,000-mL volumetric flask. Subsequently make up to the mark with water for analysis.

Preparation of a KlO₃/Kl standard solution:
Transfer 15.0 mL of the KlO₃ stock solution to a calibrated or conformity-checked 1,000-mL volumetric flask, add approx. 1 g of Kl and make up to the mark with water for analysis. 1 mL of this solution is equivalent to 0.015 mg of free chlorine.

Preparation of the chlorine standard solution:
Pipette 20.0 mL KlO₃/Kl standard solution into a calibrated or conformity-checked 100-mL volumetric flask, add
2 mL of H₂SO₄ 0.5 mol/L, leave to stand for 1 min, and then add NaOH 2 mol/L dropwise (approx. 1 ml) until the solution just loses its color. Subsequently make up the solution to the mark with water for analysis. The concentration of the solution is 3.00 mg/L free chlorine.

Stability:
The KlO₃ stock solution remains stable for 4 weeks when stored in a cool place. The KlO₃/Kl standard solution can be used for 5 hours when stored in a cool place. The dilute iodine standard solution is not stable and must be used immediately.

Materials