(e thye on' a mide).
» Ethionamide contains not less than 98.0 percent and not more than 102.0 percent of C8H10N2S, calculated on the anhydrous basis.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
Melting range: 741: between 158 and 164.
pH 791: between 6.0 and 7.0, in a 1 in 100 slurry in water.
Water, Method I 921: not more than 2.0%.
Residue on ignition 281: not more than 0.2%.
Selenium 291: 0.003%, a 200-mg test specimen being used.
Assay Transfer about 100 mg of Ethionamide, accurately weighed, to a 250-mL volumetric flask, dissolve in about 100 mL of methanol, dilute with methanol to volume, and mix. Transfer a 5-mL aliquot to a 200-mL volumetric flask, dilute with methanol to volume, and mix (test solution). Dissolve a suitable quantity of USP Ethionamide RS, accurately weighed, in methanol, and dilute quantitatively and stepwise with methanol to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 290 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of C8H10N2S in the portion of Ethionamide 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, and AU and AS are the absorbances of the test solution and the Standard solution, respectively.
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USP35NF30 Page 3129Pharmacopeial Forum: Volume No. 33(4) Page 648