Title: Limit Test for Potassium
- Objective: The limit test for potassium is provided to demonstrate that the content of Potassium does not exceed the limit given in the individual monograph in terms of ppm of potassium per gram of the test substance. The standard solution against which the comparison of opalescence is made contains 20 ppm of Potassium.
- Principle: Limit test of potassium is based on the reaction of potassium and Sodium tetraphenylborate to form opalescence.
3. Procedure:
- Preparation of Standard Solutions:
Note: All solutions should be prepared in Distilled/Purified Water.
- Potassium Standard Solution (100 ppm K): Dissolve 0.446 g of Potassium Sulfate in sufficient water and dilute to 100 ml with water. Immediately before use, dilute Dilute 1 volume of this solution to 20 volumes with water.
- Potassium Standard Solution (20 ppm K): Immediately before use, dilute Dilute 1 volume of Potassium Standard Solution (100 ppm K) to 5 volumes with water.
- Sodium Tetraphenylborate (1% w/v): Dissolve 1.0 g of Sodium Tetraphenylborate in sufficient water and dilute to 100 ml with water.
- Method:
To 10 ml of the prescribed solution add 2 ml of freshly prepared 1% w/v solution of Sodium tetraphenylborate. Prepare a standard solution in same manner using a mixture of Potassium Standard solution (20 ppm K) and 5 ml of water.
Limit: After five minutes any opalescence in the test solution is not more intense than in the standard solution.