A: To 10 mL of Oral Suspension add 15 mL of acetone, and warm to 50, with stirring, to coagulate the excipients. Filter, evaporate the acetone with the aid of a warm air blast nearly to dryness, add 10 mL of acetic acid, heat to boiling, and filter while hot. Cool the filtrate to room temperature. Filter the precipitated nitrofurantoin, and dry at 105 for 1 hour: the IR absorption 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 Identification test B under Nitrofurantoin.

for oral suspension packaged in single-unit containers: meets the requirements.

for oral suspension packaged in multiple-unit containers: meets the requirements.

pH 7.0 Phosphate buffer and Mobile phase— Prepare as directed in the Assay under Nitrofurantoin.

Internal standard solution— Dissolve about 13 mg of acetanilide in Mobile phase, dilute with Mobile phase to 200 mL, and mix.

Standard NF 250 preparation— Prepare a solution of USP Nitrofurantoin Related Compound A RS in Mobile phase to contain 125 µg per mL. [note—USP Nitrofurantoin Related Compound A RS is N-(aminocarbonyl)-N-[([5-nitro-2-furanyl]methylene)amino]glycine.] Dilute 2.0 mL of this solution with Mobile phase to 100.0 mL, and mix.

Standard nitrofurantoin preparation— Transfer about 25 mg of USP Nitrofurantoin RS, accurately weighed, to a 100-mL volumetric flask with the aid of about 50 mL of dimethylformamide. Add 20 mL of water, cool to room temperature, and dilute with dimethylformamide to volume to obtain a Standard solution. Transfer a 4.0-mL aliquot of this Standard solution to a glass-stoppered flask, add 15.0 mL of Internal standard solution, and mix.

Assay preparation— Transfer an accurately measured volume of freshly mixed Oral Suspension, equivalent to about 25 mg of nitrofurantoin, to a 100-mL volumetric flask, add 20 mL of water to the flask, and mix. Add about 50 mL of dimethylformamide, and shake the flask for about 20 minutes. Cool to room temperature, and dilute with dimethylformamide to volume. Centrifuge a portion of the solution, and transfer a 4.0-mL aliquot of the supernatant to a glass-stoppered flask. Add 15.0 mL of Internal standard, and mix. Filter a portion of the solution through a 5-µm pore size polytef filter, discarding the first few mL of the filtrate.

Test preparation— Transfer an accurately measured volume of the freshly mixed Oral Suspension, equivalent to 5 mg of nitrofurantoin, to a 100-mL volumetric flask. Dilute with Mobile phase to volume, and mix. Centrifuge a portion of this solution. Pass a portion of the supernatant through a 5-µm pore size polytef filter, discarding the first few mL of the filtrate.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with both a 254-nm detector and a 375-nm detector and a 3.9-mm × 30-cm column that contains packing L1. For the Assay, chromatograph the Standard nitrofurantoin preparation, adjusting the operating parameters so that the retention time of the nitrofurantoin peak is about 8 minutes and its peak height is about half full-scale: the relative standard deviation of the ratio of the peak responses in replicate injections is not more than 2.0%, and the resolution, R, of the acetanilide and nitrofurantoin peaks is not less than 3.5. The flow rate is about 1.2 mL per minute. For the NF 250 test, adjust the operating parameters so that the NF 250 peak has a retention time of between 3 and 6 minutes and its height is about 0.1 full-scale. The flow rate is about 1.2 mL per minute.

Procedure for limit of N-(aminocarbonyl)-N-[([5-nitro-2-furanyl]methylene)amino]glycine— Inject separately equal volumes (30 µL to 60 µL) of Standard NF 250 preparation and the Test preparation into the chromatograph, and record the peak responses with the 375-nm detector: the height of any peak appearing in the chromatogram of the Test preparation at a retention time corresponding to that of the main peak in the Standard NF 250 preparation is not greater than the height of the latter (5.0%).

Procedure for assay— Inject equal volumes (about 15 µL) of Standard nitrofurantoin preparation and the Assay preparation separately into the chromatograph, and record the peak responses with the 254-nm detector. Calculate the quantity, in mg, of C8H6N4O5 in each mL of the Oral Suspension taken by the formula: in which C is the concentration, in µg per mL, of USP Nitrofurantoin RS in the Standard solution; V is the volume, in mL, of Oral Suspension taken; and RU and RS are the ratios of the peak responses of the nitrofurantoin to the internal standard obtained from the Assay preparation and the Standard nitrofurantoin preparation, respectively.