Title: Limit Test for Chloride
- Objective: The limit test for chlorides is provided to demonstrate that the content of chlorides does not exceed the limit given in the individual monograph in terms of micrograms of chloride ions per gram of the substance being tested. The standard solution against which the comparison of opalescence is made contains 250 μg of Cl–.
- Principle: Limit test of Chloride is based on the reaction of soluble chloride with Silver Nitrate in presence of dilute Nitric Acid to form silver chloride, which appears as solid particles (Opalescence) in the solution.
3. Procedure:
- Definitions:
- Matched Tubes: Tubes that are matched as closely as possible in internal diameter and in all other respects.
- Preparation of Standard Solutions:
Note: All solutions should be prepared in Distilled/Purified Water.
- Chloride Standard Solution (25 ppm Cl): Weigh 0.0824 g of Sodium Chloride dissolve in about 70 ml of water and dilute to 100 ml with water (0.0824%w/v). Dilute 5 volume of 0.0824% w/v solution of Sodium Chloride to 100 volumes with water immediately before use.
- Dilute Nitric Acid: Dilute 10.6 ml of Nitric acid to 100 ml with
- 1 M Silver Nitrate: Dissolve 1.7 g Silver Nitrate in water and dilute up to 100 ml with water. (Preserve in Amber coloured bottle.)
- Method:
Carry out the test in matched flat-bottomed transparent glass Nessler cylinders of about 70 ml capacity and about 23 mm internal diameter bearing a 25-ml and a 50-ml mark. Dissolve the specified quantity of the substance under examination in purified water, or prepare a solution as directed in the individual monograph and transfer to a nessler cylinder. Add 10 ml of Dilute Nitric Acid (if Nitric Acid not used in test preparation) and dilute up to 50 ml with water. Add 1.0 ml of 0.1 M Silver Nitrate solution. Stir immediately with glass rod and allow to stand for 5 minutes. Protect from light.
Limit: When viewed transversely against black background any opalescence in the test solution is not more intense than that obtained by treating a mixture of 10.0 ml of Chloride standard solution (25 ppm) and 5 ml of water in the same manner.