Title: Limit Test for Sulphates
- Objective: The limit test for Sulphates is provided to demonstrate that the content of sulphate does not exceed the limit given in the individual monograph in terms of ppm of sulphate per gram of the test substance. The standard solution against which the comparison of opalescence is made contains 10 ppm of Sulphate.
- Principle: Limit test of sulphate is based on the reaction between sulphate and barium chloride solution in presence of Ethanolic sulphate standard solution to form opalescence.
3. Procedure:
- Preparation of Standard Solutions:
Note: All solutions should be prepared in Distilled/Purified Water.
- Potassium Sulphate (181% w/v): Dissolve 0.181 g of Potassium Sulphate in sufficient water and dilute to 100 ml with water.
- Sulphate Standard Solution (10 ppm SO4): Dilute 1 volume of Potassium Sulphate (181% w/v) in distilled water to 100 volumes with distilled water.
- Ethanolic Sulphate Standard Solution (10 ppm SO4): Dilute 1 volume of Potassium Sulphate (181% w/v) in ethanol (30%v/v) to 100 volumes with ethanol (30%v/v).
- Barium Chloride Solution (25% w/v): Dissolve 25.0 g of Barium Chloride in sufficient water and dilute to 100 ml with water.
- 5M Acetic acid: Dilute 28.5 ml of Glacial Acetic Acid to 100 ml with water.
- Method:
To 1.0 ml of a 25 % w/v solution of Barium Chloride in a Nessler cylinder add 1.5 ml of Ethanolic Sulphate Standard Solution (10 ppm SO4), mix and allow to stand for one minute. Add 15 ml of the solution prepared as directed in the monograph or a solution of the specified quantity of substance under examination in 15 ml of water and 0.15 ml of 5M Acetic Acid. Add sufficient water to produced 50 ml, stir immediately with a glass rod and allow to stand for five minutes.
Limit: When viewed transversely against a black background any opalescence produced in not more intense than that obtained by treating in same manner 15 ml of Sulphate Standard Solution (10 ppm SO4) in place of the solution under examination.