Identification—
Transfer a quantity of Ophthalmic Ointment, equivalent to about 200 mg of sodium chloride, to a separator containing about 25 mL of ether, and extract with 5 mL of water: the aqueous extract so obtained responds to the tests for
Sodium 
191
, and for
Chloride 191.
Assay—
Transfer an accurately weighed quantity of Ophthalmic Ointment, equivalent to about 100 mg of sodium chloride, to a separator containing about 50 mL of ether, and extract with four 20-mL portions of water. Combine the aqueous extracts in a conical flask, evaporate to a volume of about 10 mL, and add 10 mL of glacial acetic acid, 75 mL of methanol, and 0.5 mL of
eosin Y TS. Titrate, with shaking, with 0.1 N silver nitrate VS to a pink endpoint. Each mL of 0.1 N silver nitrate is equivalent to 5.844 mg of NaCl.
