by Assay
Dibasic Calcium Phosphate contains not less than 98.0 per cent and not more than 105.0 per cent of CaHPO4 (for anhydrous material) or of CaHPO4,2H2O (for the dihydrate). Weigh accurately about 0.3 g and dissolve in a mixture of 5 ml of water and 1 ml of 7 M hydrochloric acid, add 25.0 ml of 0.1 M disodium edetate and dilute to 200 ml with water. Neutralise with strong ammonia solution, add 10 ml of ammonia buffer pH 10.0 and 50 mg of mordant black 11 mixture and titrate the excess of disodium edetate with 0.1 M zinc sulphate. 1 ml of 0.1 M disodium edetate is equivalent to 0.01361 g of CaHPO4 or 0.01721 g of CaHPO4,2H2O.
