Standard preparation—
Dissolve a suitable quantity of
USP Hypromellose RS, accurately weighed, in water, and dilute quantitatively with water to obtain a solution having a known concentration of about 100 µg per mL.
Procedure—
Pipet 2 mL each of the
Standard preparation, the
Assay preparation, and water to provide a blank, into separate, glass-stoppered test tubes. To each tube add 5.0 mL of diphenylamine solution (prepared by dissolving 3.75 g of colorless diphenylamine crystals in 150 mL of glacial acetic acid and diluting the solution with 90 mL of hydrochloric acid), mix, and immediately insert the tubes into an oil bath at 105
to 110
for 30 minutes, the temperature being kept uniform within 0.1
during heating. Remove the tubes, and place them in an ice-water bath for 10 minutes or until thoroughly cool. At room temperature and using a suitable spectrophotometer, concomitantly determine the absorbances of the solutions from the
Standard preparation and the
Assay preparation at 635 nm, using the water solution as the blank. Calculate the quantity, in mg, of hypromellose in each mL of the Ophthalmic Solution taken by the formula:
0.001C(d/V)(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Hypromellose RS in the
Standard preparation; V is the volume, in mL, of Ophthalmic Solution taken;
d is the dilution factor of
V used to obtain the
Assay preparation; and
AU and
AS are the absorbances of the solutions from the
Assay preparation and the
Standard preparation, respectively.
71
:
meets the requirements.