HomePhotometry & ReflectometryAnalytical Method: Analytical Quality Assurance, Standard for Monochloramine

Analytical Method: Analytical Quality Assurance, Standard for Monochloramine

Reagents for Chlorine Standard Solution

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 approx. 13 % 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 distilled water.

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 distilled water. 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.


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.

Preparation of a 100 mg/l Chlorine Standard Solution

Prepare a chlorine standard solution of 100 mg/l Cl2 by adding the quantity according the above calculated result and fill up with water. This 100 mg/l standard is necessary for the control of Monochloramine.

Stability of the Chlorine Standard Solution

When stored in a cool place (refrigerator), the stock solution remains stable for approx. one week. The diluted investigational solutions are stable for approx. 2 hours.

Reagents for Ammonium Standard Solution

119812 Ammonium standard solution Certipur®, 1000 mg/l NH4 = 777 mg/l NH4-N
116754 Water for analysis

Preparation of the Monochloramine Standard Solution

Place 5.0 g of chlorine standard solution and 10.0 mL ammonium standard solution in a calibrated or conformity-checked 1000-mL volumetric flask and make up to the mark with distilled water. The solution prepared according to this procedure has a concentration of 5.00 mg/l Cl2 or 3.63 mg/l NH2Cl.


The solution must be used immediately.