Zinc Sulfate

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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ZnSO₄ · xH₂O

Sulfuric acid, zinc salt (1:1), hydrate;

Zinc sulfate (1:1) monohydrate 179.45 CAS RN®: 7446-19-7; UNII: PTX099XSF1.

Zinc sulfate (1:1) heptahydrate 287.54 CAS RN®: 7446-20-0; UNII: N57JI2K7WP.

Anhydrous 161.44 CAS RN®: 7733-02-0; UNII: 0J6Z13X3WO.

1 DEFINITION

Zinc Sulfate contains one or seven molecules of water of hydration. The monohydrate form contains NLT 89.0% and NMT 90.4% of zinc sulfate (ZnSO₄), corresponding to NLT 99.0% and NMT 100.5% of zinc sulfate monohydrate (ZnSO₄ · H₂O). The heptahydrate form contains NLT 55.6% and NMT 61.0% of zinc sulfate (ZnSO₄), corresponding to NLT 99.0% and NMT 108.7% of zinc sulfate heptahydrate (ZnSO₄ · 7H₂O).

2 IDENTIFICATION

A. The retention time of the zinc peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

B. Identification Tests - General 〈191〉, Chemical Identification Tests, Sulfate: Meets the requirements

3 ASSAY

Change to read:

Procedure

Diluent, Mobile phase, and (IRA 1-Jun-2024) Post-column derivatization reagent  (IRA 1-Jun-2024) : Proceed as directed in Zinc Determination 〈591〉, Procedure, Ion Chromatographic Method.

Standard solution: Equivalent to 40 μg/mL of zinc sulfate in Diluent from USP Zinc Sulfate RS

Sample solution: 44 μg/mL of zinc sulfate monohydrate or 71 μg/mL of zinc sulfate heptahydrate, equivalent to 40 μg/mL of zinc sulfate, in Diluent from Zinc Sulfate

Chromatographic system: Proceed as directed in Zinc Determination 〈591〉, Procedure, Ion Chromatographic Method, except for the Columns.

Columns

Guard: 4.0-mm × 5-cm; 9-μm packing L100. [Note - Alternatively, a 4.0-mm × 0.5-cm; 4.6-μm packing L91 column may be used.]

Analytical: 4.0-mm × 25-cm; 9-μm packing L100. [Note - Alternatively, a 4.0-mm × 25-cm; 4.6-μm packing L91 column may be used.]

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 0.73% (IRA 1-Jun-2024)

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of zinc sulfate (ZnSO₄) in the portion of Zinc Sulfate taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of zinc from the Sample solution

r_S = peak response of zinc from the Standard solution

C_S = equivalent concentration of zinc sulfate in the Standard solution (μg/mL)

C_U = concentration of Zinc Sulfate in the Sample solution (μg/mL)

Acceptance criteria

Monohydrate: 89.0%–90.4% of zinc sulfate (ZnSO₄), corresponding to 99.0%–100.5% of zinc sulfate monohydrate (ZnSO₄ · H₂O)

Heptahydrate: 55.6%–61.0% of zinc sulfate (ZnSO₄), corresponding to 99.0%–108.7% of zinc sulfate heptahydrate (ZnSO₄ · 7H₂O)

4 IMPURITIES

Arsenic 〈211〉, Procedures, Procedure 1 and Procedure 2, Procedure 1: Colorimetry

Sample solution: Dissolve a portion equivalent to 215 mg of zinc sulfate in 35 mL of water.

Acceptance criteria: NMT 14 ppm

Change to read:

Lead 〈251〉, Procedures, Procedure 1: Chemical Method

Potassium cyanide solution: Prepare as directed in 〈251〉. (IRA 1-Jun-2024)

Standard solution: Combine 5 mL of water, 0.50 mL of standard lead solution TS, and 10 mL of Potassium cyanide solution (100 mg/mL (IRA 1-Jun-2024)) in a color-comparison tube.

Sample solution: Dissolve an amount equivalent to 0.25 g of zinc sulfate in 5 mL of water, and transfer the solution to a similar, matched color-comparison tube. Add 10 mL of Potassium cyanide solution (100 mg/mL (IRA 1-Jun-2024)), and allow the mixture to become clear.

Analysis: To the Standard solution and the Sample solution add 0.1 mL of sodium sulfide TS. Mix the contents of each tube, and allow to stand for 5 min.

Acceptance criteria: Viewed downward over a white surface, the Sample solution is not darker than the Standard solution (NMT 20 ppm).

Alkalies and Alkaline Earths

Sample solution: Dissolve an amount equivalent to 1.12 g of zinc sulfate in 150 mL of water in a 200-mL volumetric flask. Add sufficient ammonium sulfide TS to precipitate the zinc completely, and dilute with water to volume. Pass through a dry filter, and discard the first portion of the filtrate.

Analysis: To 100 mL of the Sample solution filtrate add a few drops of sulfuric acid, evaporate to dryness in a tared dish, and ignite to constant weight.

Acceptance criteria: The weight of the residue is NMT 5 mg (0.9%).

5 SPECIFIC TESTS

Acidity

Sample solution: Equivalent to 28 mg/mL of zinc sulfate

Acceptance criteria: The Sample solution is not colored pink by methyl orange TS.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

Labeling: The label indicates whether it is the monohydrate or the heptahydrate. Label any oral or parenteral preparations containing Zinc

Sulfate to state the content of elemental zinc.

USP Reference Standards 〈11〉

USP Zinc Sulfate RS