Learn the limit test of sulphate through a laboratory experiment or practical.
Aim:
To perform the limit test for sulphate of the given samples as per IP 2010.
Sample: Calcium gluconate (C12H22CaO14).
Reference: Indian Pharmacopoeia (IP) 2010.
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Requirements:
Glasswares and miscellaneous: Nessler cylinder, measuring cylinder, pipette, dropper, rubber stopper, test tube stand, glass rod, and balance.
Chemicals: Calcium gluconate (C12H22Ca014), potassium sulphate (K2SO4), barium chloride (BaCl2), glacial acetic acid (CH3COOH), ethanol.
Principle of limit test for sulphate:
The limit test for sulfate relies on the reaction of SO4²- with BaCl2 in the presence of alcohol and acid (HCL or CH3COOH) to form BaSO4, which appears as solid particles in the solution. The opalescence of precipitate that is observed in the test is compared with the standard solution in dark background.
Chemical reaction:
Preparation of chemicals:
How to prepare 150 ppm sulphate standard solution:
Take 15 volume of 0.181 % w/v prepared solution of K2SO4 and dilute to 100 volume of distilled water in a volumetric flask, and properly mixing it.
How to prepare 10 ppm ethanolic sulphate standard solution:
Take 1 volume of 0.181 % w/v prepared solution of K2SO4 and dilute to 100 volume of 30 % ethanol in a volumetric flask, and properly mixing it.
How to prepare 25 % w/v barium chloride solution:
Take 25 gm of barium chloride and dilute to 70 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume with distilled water to 100 ml.
How to prepare 5 M acetic acid:
Take 28.5 ml concentrated glacial acetic acid and dilute to 100 volume of distilled water in a volumetric flask, and properly mixing it.
Procedure of limit test for sulphate:
Standard:
- Take 15.00 ml of prepared 150 ppm standard sulphate solution using a pipette into a Nessler cylinder and label it as standard.
- Add 1 ml of prepared barium chloride solution (25 % w/v).
- Allow one minute to stand after adding 1.5 ml of ethanolic sulphate standard solution.
- Then add 00.15 ml of prepared 5 M acetic acid solution.
- Add enough water to make 50 ml.
- Stir immediately with a glass rod and let stand for five minutes by protecting from light.
- Observe this standard preparation under a black background.
Test:
- Weigh exactly 01.00 gm calcium gluconate and pour 15 ml of distilled water into a Nessler cylinder and label it as a test.
- To dissolve it, you'll need to stir it for 10 to 15 minutes.
- Add 1 ml of prepared barium chloride solution (25 % w/v).
- Allow one minute to stand after adding 1.5 ml of ethanolic sulphate standard solution.
- Then add 00.15 ml of prepared 5 M acetic acid solution.
- Stir immediately with a glass rod and let stand for five minutes by protecting from light.
- Observe this test preparation under a black background and compare the opalescence of this solution to that of a standard solution.
Observations:
The calcium gluconate test solution produces less or same or more opalescence than the reference solution.
Results:
The sample passes/fails the limit test as per Indian Pharmacopoeia.
FAQ (Frequently Asked Questions):
Why HCl is used in the limit test of sulphate?
Hydrochloric acid is used in the limit test of sulphate since it helps to make the solution acidic. Under acidic conditions, phosphates and carbonates do not precipitate.
What is the importance of ethanolic sulphate solution in the sulphate limit test?
In the sulphate limit test, potassium sulphate is added to increases the sensitivity of the test, and ethanol helps prevent over-saturation of barium sulfate leading to the formation of a precipitate.
Why potassium sulphate is used in the limit test for sulphate?
To increase the test's sensitivity, potassium sulphate is used in the limit test for sulphate.
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