Aim: To perform the assay of ferrous sulphate by cerimetry.
Requirements:
- Apparatus: Beaker, Funnel, Pipette, Burette.
- Chemicals: Ferrous sulphate, Sulphuric acid, Ceric ammonium nitrate.
Monograph: Ferrous sulphate, FeSO4, 7H2O. Molecular weight 278.0
Ferrous sulphate contains not less than 98.0 per cent and not more than 105.0 per cent of FeSO4, 7H2O.
- Category: Haematinic.
- Dose: Prophylactic 300 mg; Therapeutic 600 to 900 mg daily, in divided doses (300 mg of ferrous sulphate is approximately equivalent to 60 mg of ferrous iron).
- Description: Bluish-green crystals or a light green, crystalline powder; odourless. Efflorescent in air. On exposure to moist air, the crystals rapidly oxidise and become brown.
Procedure:
(A) Standardisation of ceric ammonium nitrate:
Ammonium Ceric Nitrate, 0.1 M: Shake a solution containing 56 ml of sulphuric acid and 54.82 g of ceric ammonium nitrate for 2 minutes and carefully add five successive quantities, each of 100 ml of water, shaking after each addition. Dilute the clear solution to 1000 ml with water.
Procedure: About 0.2 gm of arsenic trioxide which was previously dried for about an hour was accurately weighed and transferred into a 500 ml conical flask.
The inner walls of the flask were washed with 100 ml of water and mixed thoroughly.
Then 300 ml of dilute sulphuric acid, 0.15 ml of osmic acid, 0.1 ml of ferroin sulphate indicator are added. Titration was carried out until the pink colour of the solution changed to pale blue or yellowish-green colour.
Each ml of 0.1 N ceric ammonium nitrate is equivalent to 4.946 grams of arsenic trioxide.
(B) Assay:
Dissolve 2.5 g of sodium bicarbonate in a mixture of 150 ml of water and 10 ml of sulphuric acid. When effervescence ceases, add about 0.5 g of the substance under examination, accurately weighed, shake gently to dissolve and titrate with 0.1 M ceric ammonium nitrate, using 0.1 ml of ferroin solution as an indicator, until the red colour disappears.
1 ml of 0.1 M ceric ammonium nitrate is equivalent to 0.02780 g of FeSO4 · 7H2O.
Observation table: (Standardization)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Ceric ammonium nitrate solution |
| 2. | Conical flask solution | Arsenic trioxide |
| 3. | Indicator | Ferroin sulphate |
| 4. | Endpoint | Green |
| Burette reading (B.R) (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Observation table: (Assay)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Ceric ammonium nitrate solution |
| 2. | Conical flask solution | Sodium bicarbonate, ferrous sulphate |
| 3. | Indicator | Ferroin |
| 4. | Endpoint | Red to colourless |
| Burette reading (B.R) (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Result: The % purity of ferrous sulphate is …….
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