Assay—
Into each of two 50-mL volumetric flasks marked
1 and
2 pipet a volume of Ophthalmic Solution, equivalent to about 2.5 mg of demecarium bromide. Into each of two additional 50-mL volumetric flasks, marked
3 and
4, pipet 5.0 mL of a freshly prepared Standard solution made by dissolving about 50 mg of
USP Demecarium Bromide RS, accurately weighed, in 100.0 mL of water. To flasks
1 and
3, add 1 N sodium hydroxide to volume, and mix. Transfer 10.0 mL of each of these solutions to separate glass-stoppered tubes, insert the stoppers loosely, heat the tubes in a water bath for 15 minutes, then cool to room temperature. The concentration of
USP Demecarium Bromide RS in the Standard solution is about 50 µg per mL. To flasks
2 and
4, add pH 10.0 alkaline borate buffer (see under
Solutions in the section
Reagents,
Indicators,
and Solutions) to volume, and mix. Concomitantly determine the absorbances of the two sodium hydroxide solutions at the wavelength of maximum absorbance at about 292 nm, with a suitable spectrophotometer, using the corresponding borate buffer solutions as the respective solvent blanks. Calculate the quantity, in mg, of C
32H
52Br
2N
4O
4 in each mL of the Ophthalmic Solution taken by the formula:
(50C / V)(AU / AS),
in which
C is the concentration, in mg per mL, of
USP Demecarium Bromide RS in the Standard solution;
V is the volume, in mL, of Ophthalmic Solution taken; and
AU and
AS are the absorbances of the sodium hydroxide solution from the Ophthalmic Solution and the Standard solution, respectively.
and 136
191
.