Ferrous Sulfate Tablets

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Ferrous Sulfate Tablets contain NLT 95.0% and NMT 110.0% of the labeled amount of ferrous sulfate heptahydrate (FeSO₄ · 7H₂O). [Note-An equivalent amount of Dried Ferrous Sulfate may be used in place of FeSO · 7H O in preparing Ferrous Sulfate Tablets.]

2 IDENTIFICATION

A. Identification Tests-General, Iron, Ferrous Salts〈191〉 and Sulfate〈191〉

Sample solution: Equivalent to 10 mg/mL of ferrous sulfate heptahydrate from powdered Tablets in water acidified with hydrochloric acid

Acceptance criteria: Meets the requirements

3 ASSAY

Procedure

Sample: Equivalent to 500 mg of ferrous sulfate heptahydrate from finely powdered Tablets (NLT 20)

Blank: Proceed as in the Analysis without the Sample.

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.1 N ceric sulfate VS

Indicator: Orthophenanthroline TS

Endpoint detection: Visual

Analysis: In a beaker, dissolve the Sample in a mixture of 20 mL of 2 N sulfuric acid and 80 mL of freshly boiled and cooled water. Filter the solution rapidly as soon as all soluble ingredients in the Tablets are dissolved, and wash the container and the filter with small portions of a mixture of 20 mL of 2 N sulfuric acid and 80 mL of freshly boiled and cooled water.

Add orthophenanthroline TS, and immediately titrate the filtrate in the suction flask with Titrant until the color changes. Perform a blank determination.

Calculate the percentage of the labeled amount of ferrous sulfate heptahydrate (FeSO₄ · 7H₂O) in the Sample taken:

Result = {[(V_S − V_B ) × N × F]/W} × 100

V_S = Titrant volume consumed by the Sample (mL)

V_B = Titrant volume consumed by the Blank (mL)

N = actual normality of the Titrant (mEq/mL)

F = equivalency factor, 278.0 mg/mEq

W = nominal weight of ferrous sulfate heptahydrate in the Sample taken (mg)

Acceptance criteria: 95.0%–110.0%

4 PERFORMANCE TESTS

Dissolution 〈711〉

Medium: 0.1 N hydrochloric acid; 900 mL

Apparatus 2: 50 rpm

Time: 45 min

Standard solution: Solution having a known concentration of iron in the Medium

Sample solution: Filtered portion of the solution under test, suitably diluted with the Medium if necessary

Instrumental conditions

(See Atomic Absorption Spectroscopy 〈852〉.)

Mode: Atomic absorption spectrophotometry

Analytical wavelength: 248.3 nm

Lamp: Iron hollow-cathode

Analysis

Samples: Standard solution and Sample solution

Determine the concentration of iron (Fe) in the Sample solution in comparison with a Standard solution.

Calculate the percentage of the labeled amount of ferrous sulfate heptahydrate (FeSO₄ · 7H₂O) dissolved:

Result = (M_r /A_r ) × (C × D × V/L) × 100

M_r = molecular weight of ferrous sulfate heptahydrate, 278.02

A_{​​​​​​​r} = atomic weight of iron, 55.85

C = measured concentration of iron in the Sample solution (mg/mL)

D = dilution factor for the Sample solution

V = volume of Medium, 900 mL

L = label claim (mg/Tablet)

Tolerances: NLT 75% (Q) of the labeled amount of ferrous sulfate heptahydrate (FeSO · 7H O) is dissolved.

Uniformity of Dosage Units 〈905〉: Meet the requirements

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

Labeling: Label the Tablets in terms of ferrous sulfate heptahydrate (FeSO · 7H O) and in terms of elemental iron.