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Analytical Method: Analytical Quality Assurance, Standard for Free Chlorine (sodium hypochlorite solution)

Preparation of a standard solution for free chlorine

Reagents:
Cat.No. 100316  Hydrochloric acid 25 % for analysis
Cat.No. 105614  Sodium hypochlorite solution (6 - 14 % active chlorine)
Cat.No. 109147  Sodium thiosulfate solution 0.1 mol/l 0.1 N solution
Cat.No. 105043  Potassium iodide for analysis
Cat.No. 105445  Zinc iodide starch solution for analysis
Cat.No. 116754  Water for analysis
 
Preparation of a stock solution of free chlorine:
First prepare a 1:10 dilution using a sodium hypochlorite solution containing approximately 6 - 14 % of active chlorine. For this pipette 10 ml of sodium hypochlorite solution into a calibrated or conformity-checked 100-ml volumetric flask and then make up to the mark with water for analysis.
 
Precise assay of the stock solution for free chlorine:
Pipette 10.0 ml of the stock solution into a 250-ml ground-glass-stoppered conical flask containing 60 ml of water for analysis. Subsequently add to this solution 5 ml of hydrochloric acid 25 %. And 3 g of potassium iodide. Close the conical flask with the ground-glass stopper, mix thoroughly, and leave to stand for 5 min. Titrate the eliminated iodine with sodium thiosulfate solution 0.1 mol/l until a weakly yellow color emerges. Add 2 ml of zinc iodide starch solution and titrate from blue to colorless.
 
Calculation:
1 ml sodium thiosulfate solution = 3.55 mg free chlorine
Further investigational concentrations may be prepared from the stock solution prepared according to the procedure described above by diluting accordingly.
 
Stability:
When stored in a cool place (refrigerator), the stock solution remains stable for approximately one week. The diluted investigational solutions are stable for approximately 2 hours.
 

For use with test kits:

 

Measuring range
in mg/l Cl2

117925

MQuantTM Chlorine Test (free chlorine)

4 - 120

117924

MQuantTM Chlorine Test (free chlorine)

25 - 500

114434

MColortestTM Chlorine Test (free chlorine)

0.01 - 0.3

111174

MColortestTM Chlorine and pH Test (free + total chlorine)

0.1 - 1.5

111100

MColortestTM Chlorine and pH Test (free + total chlorine)
refill pack for 111174

 

111113
111114

MColortestTM Chlorine Test Reagent Cl2-1 
MColortestTM Chlorine Test Reagent Cl2-2

 

111160

MColortestTM Chlorine and pH Test (free chlorine)

0.1 - 1.5

114670

MColortestTM Chlorine Test (free chlorine)

0.1 - 2

114978

MColortestTM Chlorine Test (free chlorine, liquid)

0.1 - 2

114979

MColortestTM Chlorine Test (free chlorine, liquid)
refill pack for 114978 

 

1.14801

MColortestTM Chlorine Test (free + total chlorine, liquid)

0.1 - 2

114803

MColortestTM Chlorine Test (free + total chlorine, liquid)
refill pack for 114801

 

114976

MColortestTM Chlorine Test (free chlorine)

0.25 - 15

114977

MColortestTM Chlorine Test (free chlorine)
refill pack for 114976

 

114826

MColortestTM Chlorine Test (free + total chlorine)

0.25 - 15

118326

MColortestTM Chlorine Test (free + total chlorine)
refill pack for 114826

 

116896

Reflectoquant® Chlorine Test (free + total chlorine)

0.5 - 10.0

100595

Spectroquant® Chlorine Cell Test (free chlorine)

0.03 - 6.00

100598

Spectroquant® Chlorine Test (free chlorine)

0.010 - 6.00

100086
100087

Spectroquant® Chlorine Reagents Cl2-1
Spectroquant® Chlorine Reagents Cl2-2

0.010 - 6.00

119254

Spectroquant® Chlorine Powder Packs for non-Merck photometers for 10-ml-samples (free chlorine)

0 - 2.00

119256

Spectroquant® Chlorine Powder Packs for non-Merck photometers for 25-ml-samples (free chlorine)

0 - 10.00

100597

Spectroquant® Chlorine Cell Test (free + total chlorine)

0.03 - 6.00

100599

Spectroquant® Chlorine Test (free + total chlorine)

0.010 - 6.00

 

Materials

     
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