Dissolve 18.6 g of disodium edetate in sufficient water to produce 1000 ml.
Weight accurately about 0.8 g of Granulated Zinc, dissolve by gentle warming in 12ml of diluted Hydrochloric acid and 0.1ml of bromine solution boil to remove the excess bromine, cool, add sufficient water to produce 200 ml. Pipette 20 ml in to a conical flask and nearly neutralize with 2 M sodium hydroxide. Add about 125 ml water and sufficient ammonia buffer pH 10 to dissolve the precipitate and add 5 ml in excess. Add 50 mg of mordant black II mixture and titrate with the prepared disodium edentate solution until the solution turns to green point.
Each ml of 0.1M disodium edetate solution ≡ 0.00654g of Zinc
Perform a duplicate and calculate the molarity factor (MF)
Note down the average value
MF =W x 20/200 x 0.00654 x V
W = Weight of Zinc in gram.
V = Volume of EDTA consumed in ml.
1) Discard the solution after 30 days.
2) Restandardise before use
Store in amber bottle with well fitted suitable stoppers which prevents access to atmospheric carbon dioxide.