Limit test for iron, PDF notes.

Principles and procedures involved in limit test for iron

Principle: limit test for iron depends upon the interaction of thioglycolic acid with iron in the presence of citric acid and ammonical alkaline medium, this results in the formation of purple or pink-colored ferrous salt of thioglycolic acid.

Procedure

Test solution

1. The sample is dissolved in a specific amount of water and then the volume is made up to 40ml.
2. Add 2ml of 20% w/v of citric acid
3. Add 2 drops of thioglycolic acid
4. Add ammonia to make the solution  alkaline and adjust the volume to 50ml
5. Keep aside for 5min

Standard solution

• 2ml of the standard solution of iron diluted with water up to 40 ml.
• Add 2ml of 20% w/v of citric acid
• Add 2 drops of thioglycolic acid
• Add ammonia to make the solution alkaline and adjust volume to 50ml
• Keep aside for 5min

Compare the test solution with the standard, and the test solution colour should not be more than standard.