Preparation and standardization of 0.1 N Iodine USP Volumetric Solution
1. PREPARATION :
Dissolve about 14 g of Iodine in a solution of 36 g of Potassium iodide in 100 ml of water, add 3 drops of Hydrochloric acid, dilute with water to 1000 ml.
2. STANDARDISATION :
Transfer 25.0 ml of the Iodine solution to a 250 ml flask, dilute with water to 100 ml, add 1 ml of 1 N Hydrochloric acid, swirl gently to mix, and titrate with 0.1 N Sodium Thiosulfate VS until the solution has a pale yellow colour. Add 2 ml of Starch TS and continue titrating until the solution is colourless.
Normality (N) = [Volume of Na2S2O3 (in ml) x Normality of Na2S2O3]/25
Limit : 0.1 N ± 5 % (0.0950 N – 0.1050 N)
3. PREPARATION OF INDICATORS / REAGENTS :
a. 1 N Hydrochloric acid VS:
Dilute 8.5 ml of Hydrochloric acid with water to 100 ml.
b. 0.1 N Sodium Thiosulfate VS:
Preparation and Standardisation as per Doc. Ref. No.: D/VS/USP/005
c. Starch TS:
Mix 1 g of soluble starch with 10 mg of red Mercuric Iodide and sufficient cold water to make a thin paste. Add 200 ml of boiling water, and boil for 1 minute with continuous stirring. Cool, and use only the clear solution.
Note: Commercially available, stabilized starch indicator solution may be used.
4. STORAGE CONDITION :
Preserve in amber-coloured, glass-stoppered bottles.