Analytical Method: Analytical Quality Assurance, Standard for COD/Chloride

Reagents:
Cat.No. 102400 Potassium hydrogen phthalate for analysis, volumetric standard
Cat.No. 106406 Sodium chloride Suprapur^®
Cat.No. 116754 Water for analysis

Preparation of a chloride dilution solution:
Dissolve 32.9 g of sodium chloride (free from organic material, e. g. Suprapur^®) in a calibrated or conformity-checked 1000-ml volumetric flask and make up to the mark with distilled water. The stock solution prepared according to this procedure has a concentration of 20 g/l Cl^-.

Preparation of a COD standard solution:
Dissolve 0.851 g of potassium hydrogen phthalate in a calibrated or conformity-checked 100-ml volumetric flask and make up to the mark with dilution solution. The stock solution prepared according to this procedure has a concentration of 10 000 mg/l COD and 20 g/l Cl^-. Further investigational concentrations may be prepared from this standard solution by diluting accordingly with dilution solution.

Stability:
When stored in a cool place (refrigerator), the dilution solution of 20 g/l Cl^- and the standard solution of 10 000 mg/l COD / 20 g/l Cl^- remain stable for one month. When stored under appropriate cool conditions (refrigerator), the diluted investigational solutions remain stable - depending on the respective concentration - for approximately one week to one month.