Assay of Calcium gluconate IP Pharmaceutical Analysis I Practical

Pharmaceutical Analysis I Practical: Limit test for (1) Chloride (2) Sulphate (3) Iron (4) Arsenic Preparation and standardisation of (1) Sodium hydroxide (2) Sulphuric acid (3) Sodium thiosulfate (4) Potassium permanganate (5) Ceric ammonium sulphate Assay (1) Ammonium chloride (2) Ferrous sulphate(3) Copper sulphate (4) Calcium gluconate (5) Hydrogen peroxide (6) Sodium benzoate (7) Sodium Chloride Determination of Normality (1) Conductometric titration of strong acid against a strong base (2) Conductometric titration of strong acid and weak acid against a strong base (3) Potentiometric titration

assay of calcium gluconate by complexometric titration

Aim

To determine per cent content of Calcium gluconate in a given sample / To perform the assay of calcium gluconate

Principle

Calcium gluconate can be assayed using complexometric titrations of Ca²⁺ ions using EDTA as a sequestering (chelating) agent which results in the formation of a relatively stable complex. However, Mordant-Black II which is used as an indicator does not give distinct colour change. Hence, calcium ions are not directly titrated against disodium EDTA. Rather a displacement or replacement type of titration is used or performed wherein, a known volume of 0.05M magnesium sulphate solution is added (5ml) which acts as a displacing agent.

Magnesium ions displace calcium ions from the calcium indicator complex and form a more stable Mg indicator complex. But this complex is less stable than the Mg-EDTA complex. Relative stability of different complexes decreases in following order: Ca-EDTA > Mg-EDTA > Mg-In > Ca-In. Initially when both calcium and magnesium ions are present in the solution and when the indicator is added it forms a complex with Mg as Mg-In is stronger than Ca-In complex and imparts a pink colour to the solution.

When titration commences added EDTA forms a complex with calcium ions as a Ca-EDTA complex is stronger than the Mg-EDTA complex. when all the calcium ions are complexed than free Mg++ forms complex with EDTA and the endpoint is reached then Mg-In complex breaks liberating free Mg+2 and In- which forms complex with EDTA and free In- imparts a blue colour to the solution. The ammonia solution buffers the solution at a pH 10

Standard

Calcium gluconate (mol. wt.: 448.4) contains not less than 98.5% and not more than 102.0% of C12H22CaO14, H2O.

Procedure

Preparation of 0.1M disodium edetate solution

Dissolve ______ g of disodium edetate in sufficient water to produce 1000ml

Standardization of 0.1M disodium edetate solution

Weigh accurately about 0.8 g of granulated zinc dissolved by gentle warming in 12 ml of dil. Hydrochloric acid and 0.1ml of bromine water.
Boil to remove excess bromine, cool and add sufficient water to produce 200ml. pipette 20 ml of the resulting solution into a flask and nearly neutralize with 2M sodium hydroxide.
Dilute to about 150ml with water add sufficient ammonia buffer pH 10.0 to dissolve the precipitate and add 5ml in excess.
Add 50mg of mordant black II mixture and titrate with the disodium edetate solution until the solution turns green.