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.

Materials
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