Limit Test for Potassium and Sulphates : Pharmaguideline

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Limit Test for Potassium and Sulphates

Learn how to test the Potassium and Sulphates color comparison method in Pharmaceutical substances.


To 10 ml of the prescribed solution add 2 ml of a freshly prepared 1 percent w/v solution of sodium tetraphenyl borate. Prepare a standard solution, in the same manner, using a mixture of potassium standard solution (20 ppm K) and 5 ml of water. After 5 minutes, any opalescence in the test solution is not more intense than in the standard solution.


NOTE - The solutions used for this test should be prepared with distilled water.
To 1.0 ml of a 25.0 per cent w/v solution of barium chloride in a Nessler cylinder add 1.5 ml of ethanolic sulfate standard solution (10 ppm SO4 ), mix and allow to stand for 1 minute. Add 15 ml of the solution prepared as directed in the monograph or a solution of the specified quantity of the substance under examination in 15 ml of water and 0.15 ml of 5 M acetic acid. Add sufficient water to produce 50 ml, stir immediately with a glass rod and allow standing for 5 minutes.

When viewed transversely against a black background any opalescence produced is not more intense than that obtained by treating in the same manner 15 ml of sulfate standard solution (10 ppm SO4) in place of the solution under test.

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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