Hydroxy Naphthol Blue

Dibasic calcium phosphate 0.2 g Hydroxy naphthol blue Each ml of 0.05 M disodium edetate = 0.002004 g of Ca... 

The USP [2] recommends a titrimetric method for the determination of EDTA using chelometric standard calcium carbonate previously dried at 110°C for 2 hours, and hydroxy naphthol blue as the indicator. The weight of EDTA (in mg) is calculated by the formula ... 

Assay Dissolve about 300 mg of sample, accurately weighed, in 150 mL of water containing 2 mL of 2.7 N hydrochloric acid. While stirring, preferably with a magnetic stirrer, add about 30 mL of 0.05 M disodium EDTA from a 50-mL buret, then add 15 mL of 1 A sodium hydroxide and 300 mg of hydroxy naphthol blue indicator, and continue the titration to a blue endpoint. Each milliliter of 0.05 M disodium EDTA is equivalent to 7.909 mg of Ca(C2H302)2. 

Hydroxy Naphthol Blue The disodium salt of l-(2-naph-tholazo-3,6-disulfonic acid)-2-naphthol-4-sulfonic acid deposited on crystals of sodium chloride. Small blue crystals, freely soluble in water. In the pH range between 12 and 13, its solution is red-pink in the presence of calcium ion and deep blue in the presence of excess disodium EDTA. 

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