Assay of Sodium benzoate by non-aqueous titration
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
Aim
To determine the percent purity of Sodium benzoate in a given sample.
Principle
Alkaline and alkali earth salts of organic acid function as bases in presence of acetic acid solution. Potassium hydrogen phthalate is used as a primary standard. It reacts with perchloric acid where the Potassium hydrogen phthalate acts as a base and perchloric acid as acid. It is a nonaqueous titration. Sodium benzoate is a weakly basic drug that does not react with the acid in an aqueous medium strongly and gives an unsatisfactory endpoint. In a nonaqueous medium, the endpoint is satisfactory. therefore glacial acetic acid is used as a solvent for the reaction between sodium benzoate and perchloric acid. The endpoint is determined using 1-naphtholbenzein as an indicator.
Standard
Sodium Benzoate contains not less than 99.0 percent and not more than 100.5 percent of C7H5NaO2, calculated on a dried basis.
Procedure
Weigh accurately about 0.25 g, dissolve in 20 ml of anhydrous glacial acetic acid, warming to 50º if necessary, cool. Titrate with 0.1 M perchloric acid, using 0.05 ml of 1-naphtholbenzein solution as indicator. Carry out a blank titration.
Reference
Indian Pharmacopoeia,2007, volume1, Pg no 1081
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