Identification—
A:
The solution of Tablets employed for measurement of absorbance in the Assay exhibits an absorbance maximum at 290 ± 2 nm.
B:
Digest a quantity of powdered Tablets, equivalent to about 1 g of ethionamide, with 50 mL of methanol, and filter through a medium-porosity, sintered-glass funnel. Evaporate the filtrate on a steam bath to dryness: the residue so obtained melts between 155
and 164
.
Dissolution 
711
—
Medium:
0.1 N hydrochloric acid; 900 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
8H
10N
2S dissolved by employing UV absorption at the wavelength of maximum absorbance at about 274 nm on filtered portions of the solution under test, suitably diluted with
Medium, if necessary, in comparison with a Standard solution having a known concentration of
USP Ethionamide RS in the same
Medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C8H10N2S is dissolved in 45 minutes.
Assay—
Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of ethionamide, to a medium-porosity, sintered-glass funnel that is fitted into a 250-mL suction flask. Extract the specimen by stirring it with successive 10-mL portions of methanol, using a total of about 100 mL of solvent, drawing off each portion of liquid with gentle suction before adding the next portion. Transfer the combined methanol extracts to a 250-mL volumetric flask, dilute with methanol to volume, and mix. Proceed as directed in the
Assay under
Ethionamide, beginning with “Transfer a 5-mL aliquot.” Calculate the quantity, in mg, of C
8H
10N
2S in the portion of Tablets taken by the formula:
10C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Ethionamide RS in the Standard solution, calculated on the anhydrous basis, and
AU and
AS are the absorbances of the solution of Ethionamide Tablets and the Standard solution, respectively.
