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Limit Test of Sulphate

Principle:

Limit test of sulphate is based on the reaction of soluble sulphate with barium chloride in presence of dilute hydrochloric acid to form barium sulphate which appears as solid particles (turbidity) in the solution.



Procedure:

Test sample Standard compound
Specific weight of compound is dissolved in water or solution is prepared as directed in the pharmacopoeia and transferred in Nessler cylinder Take 1ml of 0.1089 % W/V solution of potassium sulphate in Nessler cylinder
Add 2ml of dilute hydrochloric acid Add 2ml of dilute hydrochloric acid
Dilute to 45 ml in Nessler cylinder Dilute to 45 ml in Nessler cylinder
Add 5ml of barium sulphate reagent Add 5ml of barium sulphate reagent
Keep aside for 5 min Keep aside for 5 min
Observe the Turbidity Observe the Turbidity

Barium sulphate reagent contains barium chloride, sulphate free alcohol and small amount of potassium sulphate.

Observation:

The turbidity produce in sample solution should not be greater than standard solution. If turbidity produces in sample solution is less than the standard solution, the sample will pass the limit test of sulphate and vice versa.

Reasons:

Hydrochloric acid helps to make solution acidic.
Potassium sulphate is used to increase the sensitivity of the test by giving ionic concentration in the reagent
Alcohol helps to prevent super saturation.

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