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XXII
Release 05/04
Standard solution of COD
Preparation of a standard solution:
Dissolve 0.850 g of potassium hydrogen phthalate
GR in a calibrated or conformity-checked 1000-ml
volumetric flask and make up to the mark with
distilled water. The stock solution prepared accor-
ding to this procedure has a concentration of
1000 mg/l COD.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
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Stability:
When stored in a cool place (refrigerator), the
stock solution remains 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.
▼
Reagents required:
1.02400.0080 Potassium hydrogen phthalate GR
for analysis, volumetric standard
1.16754.9010 Water GR for analysis
Instructions for the Preparation of Standard Solutions
Standard solution of chlorine dioxide
acc. to DIN EN ISO 7393
Preparation of a KlO
3
stock solution:
Dissolve 1.005 g of KlO
3
in 250 ml of distilled
water in a calibrated or conformity-checked
1000-ml volumetric flask. Subsequently make up
to the mark with distilled water.
▼
Preparation of a KlO
3
/Kl standard solution:
Transfer 10.5 ml of the KlO
3
stock solution to a
calibrated or conformity-checked 1000-ml
volumetric flask, add approx. 1g of Kl and make
up to the mark with distilled water.
1 ml of this solution is equivalent to 0.020 mg
of chlorine dioxide.
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Preparation of the chlorine dioxide
standard solution:
Pipette 10 ml KlO
3
/Kl standard solution into a
calibrated or conformity-checked 100-ml
volumetric flask, add 2.0 ml of H
2
SO
4
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 colour. Subsequently make up the
solution to the mark with distilled water.
The concentration of the solution is 2.00 mg/l
chlorine dioxide.
▼
Stability:
The KlO
3
stock solution remains stable for 4
weeks when stored in a cool place. The KlO
3
/Kl
standard solution can be used for 5 hours when
stored in a cool place. The dilute chlorine dioxide
standard solution is not stable and must be used
immediately.
▼
Reagents required:
1.02404.0100 Potassium iodate, volum. standard
1.05043.0250 Potassium iodide GR for analysis
1.09072.1000 Sulfuric acid 0.5 mol/l
1.09136.1000 Sodium hydroxide solution 2 mol/l
1.16754.9010 Water GR for analysis