Dr E. Ramanathan PhD
Determination of Iron in a Zinc Phosphate Coating Bath can be done by the following titrimetric or spectrophotometric methods. A commonly used method is titration with potassium dichromate in acidic medium using diphenylamine sulfonate as an indicator.
1. Reagents Required:
- 1 N H₂SO₄ (Sulfuric acid)
- 0.1 N K₂Cr₂O₇ (Potassium dichromate standard solution)
- Diphenylamine sulfonate indicator
- Distilled water
2. Procedure (Titrimetric Method):
- Sample Preparation:
- Take 10 mL of well-mixed phosphate bath sample.
- Dilute with ~50 mL distilled water in a 250 mL conical flask.
- Acidification:
- Add 10 mL of 1:1 H₂SO₄ carefully. The solution should be strongly acidic.
- Indicator Addition:
- Add 2–3 drops of diphenylamine sulfonate indicator. The solution turns greenish.
- Titration:
- Titrate with 0.1 N potassium dichromate until the color changes from green to violet-blue endpoint.
Alternative Method (UV-Vis Spectrophotometry):
- Colorimetric analysis using 1,10-phenanthroline complex at ~510 nm.
- Suitable for Fe²⁺ analysis after reduction of Fe³⁺ to Fe²⁺ with hydroxylamine hydrochloride.
Additional References
Guidelines to Volumetric Calculations
