» Dichlorphenamide Tablets contain not less than 92.0 percent and not more than 108.0 percent of the labeled amount of C6H6Cl2N2O4S2.
Packaging and storage Preserve in well-closed containers.
USP Reference standards 11
USP Dichlorphenamide RS
A: The polarogram of the solution employed for measurement in the Assay exhibits a half-wave potential (E½) within 1% of that of USP Dichlorphenamide RS, similarly measured (E½ is about 1.42 volts against a saturated calomel electrode).
B: Fuse a quantity of powdered Tablets, equivalent to 200 mg of dichlorphenamide, with 1 pellet of sodium hydroxide: the ammonia fumes produced cause moistened red litmus paper to turn blue. The fusion mixture responds to the tests for Sulfite 191.
Medium: 0.1 M pH 8.0 phosphate buffer (see Buffer Solutions in the section Reagents, Indicators, and Solutions); 900 mL.
Apparatus 2: 75 rpm.
Time: 60 minutes.
Procedure Determine the amount of C6H6Cl2N2O4S2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 285 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium in comparison with a Standard solution having a known concentration of USP Dichlorphenamide RS in the same Medium.
Tolerances Not less than 80% (Q) of the labeled amount of C6H6Cl2N2O4S2 is dissolved in 60 minutes.
Uniformity of dosage units 905: meet the requirements.
Assay Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of dichlorphenamide, to a 50-mL volumetric flask. Add about 40 mL of dimethylformamide, shake for 5 minutes to dissolve the dichlorphenamide, and add dimethylformamide to volume. Pipet 10 mL of this suspension into a 100-mL volumetric flask, add 25.0 mL of 0.1 N tetramethylammonium bromide, and dilute with water to volume. Transfer a portion of this solution to a polarographic cell that is immersed in a water bath regulated at 24.5 to 25.5. Deaerate by bubbling purified nitrogen through the solution for 5 minutes. Insert the dropping mercury electrode of a suitable polarograph, and record the polarogram from 0.80 volt to 1.80 volts, using a saturated calomel electrode as the reference electrode, and a galvanometer having a sensitivity of about 5 microamperes full scale. Determine the height of the diffusion current at 1.65 volts. Calculate the quantity, in mg, of C6H6Cl2N2O4S2 in the portion of Tablets taken by the formula:
500C[(id)U / (id)S]in which (id)U is the observed diffusion current of the assay solution and (id)S is that determined similarly in a solution of USP Dichlorphenamide RS the concentration of which is C mg per mL (about 100 µg per mL).
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USP35NF30 Page 2877