Zinc Sulfate – Zinc Sulfat – Zinc Sulphate – Zinci sulfas

ZnSO4,H2O (monohydrate); ZnSO4,7H2O (heptahydrate)
Relative molecular mass. 179.5 (monohydrate); 287.5 (heptahydrate).
Chemical name. Zinc sulfate monohydrate; CAS Reg. No. 7446-19-7 (monohydrate). Zinc sulfate heptahydrate; CAS Reg. No.
7446-20-0 (heptahydrate).
Description. A white or almost white, crystalline powder, or colourless, transparent crystals.
Solubility. Very soluble in water, practically insoluble in ethanol (~750 g/l) TS.
Category. Adjunct to oral rehydration salts in( prevention and) treatment of dehydration due to diarrhoea; astringent.
Storage. Zinc sulfate should be kept in a well-closed, non-metallic container.
Labelling. The designation on the container should state whether the substance is in the monohydrate or heptahydrate form and,
where appropriate, that it is suitable for use in the manufacture of parenteral dosage forms.
Requirements
Definition. Zinc sulfate monohydrate contains not less than 99.0% and not more than 101.0% of ZnSO4,H2O. Zinc sulfate
heptahydrate contains not less than 99.0% and not more than 104.0% of ZnSO4,7H2O.
Identity tests
A. Dissolve 0.25 g in 5 mL of water R and add 0.2 mL of sodium hydroxide (400 g/l) TS. A white precipitate is
formed. Add a further 2 mL of sodium hydroxide (400 g/l) TS. The precipitate dissolves. Add 10 mL of ammonium
chloride (100 g/l) TS. The solution remains clear. Add 0.1 mL of sodium sulfide TS. A flocculent white precipitate is
formed.
B. A 50 mg/mL solution yields the reactions described under 2.1 General identification tests as characteristic of
sulfates.
C. The test substance complies with the limits of the assay.
pH value (1.13). pH of a 50 mg/mL solution in carbon-dioxide-free water R, 4.4-5.6.
Clarity and colour of solution. If intended for use in the manufacture of parenteral preparations, a 50 mg/mL solution in carbondioxide-
free water R is clear and colourless.
Chlorides. Use 0.83 g in 20 mL for the preparation of the test solution as described under 2.2.1 Limit test for chlorides; not more
than 300 μg/g.
Iron. Use 0.40 g for the preparation of the test solution as described under 2.2.4 Limit test for iron; not more than 100 μg/g.
Lead. Dissolve 0.25 g (or an amount of the substance equivalent to 0.25 g of ZnSO4) in 5 mL of water R and transfer to a suitable
colour comparison tube (tube A). Add 10 mL of potassium cyanide solution (100 g/L) TS, mix and allow the mixture to become
clear. In a second matched tube (tube B), to 5 mL of water R add 0.5 mL of dilute lead PbTS and 10 mL of potassium cyanide
solution (100 g/L) TS. Add 0.1 mL of sodium sulphide (100 g/L) TS to each tube, mix and allow to stand for 5 minutes. Compare
the solutions as described under 1.11.1 Colour of liquids; the colour of the solution in tube A is not more intense than the solution
in tube B (20μg/g).
Assay
For the monohydrate Dissolve about 80 mg, accurately weighed, in 5 mL of acetic acid (~120 g/l) TS and proceed with the
titration as described under 2.5 Complexometric titrations for zinc. Each mL of disodium edetate (0.05 mol/l) VS is equivalent to
8.975 mg of ZnSO4,H2O.
For the heptahydrate Dissolve about 0.13 g, accurately weighed, in 5 mL of acetic acid (~120 g/l) TS and proceed with the
titration as described under 2.5 Complexometric titrations for zinc. Each mL of disodium edetate (0.05 mol/l) VS is equivalent to
14.38 mg of ZnSO4,7H2O.