Extract 10 mL of it with 25 mL of chloroform, filter the chloroform extract through dry, folded filter paper, and evaporate the filtrate to dryness: the residue so obtained responds to Identification test A under Tropicamide.
The UV absorption spectrum of the solution employed for measurement of absorbance in the Assay
exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Tropicamide RS
, concomitantly measured.
Transfer an accurately measured volume of Ophthalmic Solution, equivalent to about 30 mg of tropicamide, to a 100-mL volumetric flask, add water to volume, and mix. Transfer 10.0 mL of this solution to a separator, add 2 mL of sodium carbonate solution (1 in 10), extract with four 20-mL portions of chloroform, and combine the extracts in a second separator. Wash the combined extracts with a 25-mL portion of pH 6.5 phosphate buffer (see Buffer Solutions
in the section Reagents, Indicators, and Solutions
), and transfer to another separator. Wash the aqueous layer with 10 mL of chloroform, and add it to the extracts. Extract the chloroform solution with four 20-mL portions of dilute sulfuric acid (1 in 6), combine the acid extracts in a 100-mL volumetric flask, and add the dilute acid to volume. Dissolve an accurately weighed quantity of USP Tropicamide RS
in dilute sulfuric acid (1 in 6), and dilute quantitatively and stepwise with the same solvent to obtain a Standard solution having a known concentration of about 30 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 253 nm, with a suitable spectrophotometer, using dilute sulfuric acid (1 in 6) as the blank. Calculate the quantity, in mg, of C17
in each mL of the Ophthalmic Solution taken by the formula:
(C / V)(AU / AS),
in which C
is the concentration, in µg per mL, of USP Tropicamide RS
in the Standard solution, V
is the volume, in mL, of Ophthalmic Solution taken, and AU
are the absorbances of the solution from the Ophthalmic Solution and the Standard solution, respectively.