Limit Test for Sulphate | How to Perform Limit Test for Sulphate | सलफेट लिमिट टेस्ट कैसे करते हैं

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LIMIT TEST FOR SULPHATES
Limit = a value or amount that is likely to be present in a substance
Test = to examine or to investigate
Impurities = a foreign matter present in a compound

Limit test is defined as quantitative or semi quantitative test designed to identify and control small quantities of impurity which is likely to be present in the substance.

Limit test is generally carried out to determine the inorganic impurities present in compound. In short, limit test is nothing but to identify the impurities present in the substance and compare it with standard.

Importance of Limit tests:
To find out the harmful amount of impurities
To find out the avoidable/unavoidable amount of impurities

Apparatus Required
Nessler cylinders, Glass rod ,stand

Chemicals Required
1. Dilute Hydrochloric acid
2. Barium sulphate reagent. Mix 15ml of 0.5M BaCl2, 55ml of water and 20ml of sulphate free alcohol and add 5 ml of 0.0181% w/v potassium sulphate. Dilute to 10ml with water and mix. 0.5M BaCl2 Barium chloride in 1000 ml of water.

Principle:
It is based upon the chemical reaction between Barium chloride and soluble sulphate in presence of dilute Hydrochloric acid . The turbidity produced is compared with the standard solution. Barium sulphate reagent contains barium chloride, sulphate – free alcohol and small quantity of potassium sulphate. The inclusion of the small quantity of potassium sulphate in the reagent increases the sensitivity of the test. Alcohol prevents super saturation and more uniform turbidity develops. If the turbidity produced in the test is more intense than the standard turbidity it fails the test. Otherwise, it passes the test.

Standard compound
1. Take 1ml of 0.1089 % W/V solution of potassium sulphate in Nessler cylinder.
2. Add 2ml of dilute hydrochloric acid
3. Dilute to 45 ml in Nessler cylinder
4. Add 5ml of barium sulphate reagent.
5. Keep aside for 5 min
6. Observe the Turbidity

Test sample
1. Specific weight of compound is dissolved in water or solution is prepared as directed in the pharmacopoeia and transferred in Nessler cylinder.
2. Add 2ml of dilute hydrochloric acid.
3. Dilute to 45 ml in Nessler cylinder
4. Add 5ml of barium sulphate reagent
5. Keep aside for 5 min.
6. Observe the Turbidity

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