LIMIT TEST FOR CHLORIDES
Limit test is defined as a quantitative or semiquantitative test designed to identify and control a small amount of inorganic impurities which is likely to be present in the substance. Limit test is nothing but to identify impurities in the substance and compare with the standard.
- Nessler cylinders
- Glass rod
- Dilute Nitric acid (10%)
- Silver nitrate (5%)
- Sodium chloride
It is based upon the chemical reaction between silver nitrate and soluble chlorides in the presence of dilute nitric acid to give opalescence of silver chloride. If the Opalescence produced is compared with the standard solution. If the opalescence in the sample is less than the standard, it passes the test. If it is more than the standard, it fails the test.
|Test sample||Standard compound|
|1. Specific weight of the compound is dissolved in water or solution is prepared as directed in the pharmacopoeia and transferred in Nessler cylinder.||1. Take 1ml of 0.05845 % W/V solution of sodium chloride in Nessler cylinder.|
|2. Add 10ml of dilute nitric acid||2. Add 10 ml of dilute nitric acid|
|3. Dilute to 50ml in Nessler cylinder||3. Dilute to 50ml in Nessler cylinder|
|4. Add 1ml of AgNO3 solution||4. Add 1ml of AgNO3 solution|
|5. Keep aside for 5 min||5. Keep aside for 5 min|
|6. Observe the Opalescence/Turbidity||6. Observe the Opalescence/Turbidity|
The opalescence produces in sample solution should not be greater than the standard solution. If opalescence produces in a sample solution is less than the standard solution, the sample will pass the limit test of chloride and visa versa.
Nitric acid is added in the limit test of chloride to make solution acidic and helps silver chloride precipitate to make solution turbid at the end of process.
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