Identification—
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
.
Dissolution 711—
Apparatus 2:
75 rpm.
Time:
60 minutes.
Procedure—
Determine the amount of C
6H
6Cl
2N
2O
4S
2 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.
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 C
6H
6Cl
2N
2O
4S
2 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).
