Limit of Iron

Limit of Iron

Summary Purpose: Verify iron content does not exceed the specified limit. Principle: The monograph describes reduction and complexation steps that produce a colored species which is compared to a blank or limit standard; absence of color beyond the blank indicates compliance.

Step-by-Step Instructions

1. Add citric acid and thioglycolic acid to the sample solution.

2. Make the solution alkaline with stronger ammonia water.

3. Wait 5 minutes and compare the pink color to a standard iron solution.

Acceptance Criteria

• Any pink color in the test solution is not more intense than the standard (NMT 2 ppm).

Tips

• Use freshly prepared reducing reagent and run a positive control at the limit to confirm sensitivity.

• If turbidity or particulate matter is present, filter as directed by the monograph before color development.

Cautions

• Thioglycolic acid and some reducing agents are odorous and can be hazardous; handle in a fume hood with PPE.

• Dispose of iron‑containing wastes according to local regulations.