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.