Packaging and storage—
Preserve in tight containers.
Identification—
It responds to the tests for
Zinc 
191
and for
Sulfate 191.
pH 791:
between 5.8 and 6.2; or, if it contains sodium citrate, between 7.2 and 7.8.
Assay—
Pipet into a beaker a volume of Ophthalmic Solution, equivalent to about 25 mg of zinc sulfate. Add 1 mL of glacial acetic acid, and adjust by the dropwise addition of 6 N ammonium hydroxide to a pH of between 5.0 and 5.5. Add 1 drop of copper ethylenediaminetetraacetate solution [prepared by mixing 1 mL of cupric sulfate solution (1 in 40) and 1 mL of 0.1 M edetate disodium] and 3 drops of a 1 in 1000 solution of 1-(2-pyridylazo)-2-naphthol in anhydrous methanol, and titrate with 0.01 M edetate disodium VS. Each mL of 0.01 M edetate disodium is equivalent to 1.614 mg of ZnSO4.
