Limit Test for Sulphate

Principle for Limit Test for Sulphate

Limit Test for Sulphate is based upon the chemical reaction between barium chloride and soluble sulphate in the presence of dilute hydrochloric acid. The turbidity produced is compared with the standard solution. Barium chloride reagent contains barium chloride, sulphate-free alcohol and a small quantity of potassium sulphate. The inclusion of a small quantity of potassium sulphate in the reagent increases the sensitivity of the test. Alcohol prevents supersaturation and more uniform turbidity develops. If the turbidity produced in the test is more intense than the standard turbidity, then the drug fails the test, otherwise, it passes the test.

Apparatus Required

• Nessler cylinders
• Glass rod
• Stand

Chemicals Required for Limit Test for Sulphate

• Dilute hydrochloric acid
• 0.5 M Barium chloride: 122.1 g of BaCl₂. 2H₂O dissolved in distilled water.
• Barium sulphate reagent containing 0.5 M barium chloride in 1000 ml of water. (This is prepared as follows: Mix 15 ml of 0.5 M BaCl2, 55 ml of water and 20 ml of sulphate free alcohol. Add 5 ml of 0.0181% w/v potassium sulphate. Dilute to 10 ml with water and mix.)

Procedure for Limit Test for Sulphate

Take two 50 ml Nessler cylinders. Label one as “Test” and the other as “Standard”

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