Millipore Spectroquant Multy Operating Manual page 210

Standard solution of free chlorine
Preparation of a stock solution:
First prepare a 1:10 dilution using a sodium hypochlorite so-
lution containing approximately 13 % of active chlo rine. For
this pipette 10 ml of sodium hypochlorite solution into a cali-
brated or confor mity-checked 100-ml volumetric flask and
then make up to the mark with distilled water.
Precise assay of the stock solution:
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 solu tion 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 1 min.
Titrate the eliminated iodine with sodium thiosul fate 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 and preparation of the standard solution:
Consumption of sodium thiosulfate solution 0.1 mol/l (ml) x 355 =
= content of free chlorine, in mg/l
Further investigational concentrations may be prepared from
the stock solution prepared according to the procedure de-
scribed above by diluting accordingly with distilled water.
Stability:
When stored in a cool place (refrigerator), a standard solution
of 1000 mg/l remains stable for approximately one week. The
diluted standard solutions (investigational concentrations)
are stable for approximately 2 hours.
Reagents required:
1.00316.1000 Hydrochloric acid
25 % for analysis
EMSURE®
1.05614.9025 Sodium hypochlorite
solution techn.
approx. 13 % active
chlorine
1.09147.1000 Sodium thiosulfate
solution 0.1 mol/l
Titripur®
1.05043.0250 Potassium iodide GR
for analysis
1.05445.0500 Zinc iodide-starch
solution GR for
analysis
1.16754.9010 Water for analysis
EMSURE®
Note
This is a standard solution that is
absolutely necessary for the prepa-
ration of the monochloramine stan-
dard.
Chapter 5.2 | Page 10 of 23