A: Add 10mLof 6Nacetic acid to a quantity of powdered Tablets,equivalent to about 100mg of nitrofurantoin,boil for a few minutes,and filter while hot.Cool to room temperature,collect the precipitate of nitrofurantoin,and dry at 105for 1hour:the IRabsorption spectrum of a mineral oil dispersion of the precipitate so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Nitrofurantoin RS.

B: It responds to Identificationtest Bunder Nitrofurantoin.

Medium: pH7.2phosphate buffer (see Buffer Solutionsin the section Reagents,Indicators,and Solutions);900mL.

Apparatus 1: 100rpm.

Times: 60minutes,120minutes.

Standard preparation— Dissolve about 50mg,accurately weighed,of USP Nitrofurantoin RSin 25mLof dimethylformamide,dilute with Dissolution Mediumto 500mL,mix,and dilute a suitable aliquot of the resulting solution with Dissolution Mediumto obtain a solution having a known concentration of about 10µg per mL.

Procedure— Determine the amount of C8H6N4O5dissolved from absorbances at the wavelength of maximum absorbance at about 375nm of filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,using Dissolution Mediumas the blank,in comparison with the Standard preparation.

Tolerances— Not less than 25%(Q)of the labeled amount of C8H6N4O5is dissolved in 60minutes,and not less than 85%(Q)of the labeled amount of C8H6N4O5is dissolved in 120minutes.

pH7.0phosphate buffer,Mobile phase,Internal standard solution,Standard preparation,andChromatographic system— Proceed as directed in the Assayunder Nitrofurantoin.

Assay preparation— Weigh and finely powder not less than 20Tablets.Weigh accurately a portion of the powder,equivalent to about 50mg of nitrofurantoin,into a glass-stoppered flask.Add 40.0mLof dimethylformamide,and shake by mechanical means for 15minutes.Add 50.0mLof Internal standard solution,mix,and cool to room temperature.Pass a portion of the solution through a 0.45-µm pore size nylon filter,discarding the first few mLof the filtrate.

Procedure— Proceed as directed for Procedurein the Assayunder Nitrofurantoin.Calculate the quantity,in mg,of C8H6N4O5in the portion of the powder taken by the formula: in which Wis the weight,in mg,of USP Nitrofurantoin RSin the Standard preparationand RUand RSare the ratios of the peak responses of the nitrofurantoin to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.