A: Triturate a quantity of finely powdered Tablets, equivalent to about 500 mg of sulfamethizole, with 5 mL of chloroform, and transfer to a small filter. Wash with another 5-mL portion of chloroform, and discard the filtrate. Triturate the residue with 10 mL of 6 N ammonium hydroxide for 5 minutes, add 10 mL of water, filter, and proceed as directed in the Identification test under Sulfamethizole Oral Suspension, beginning with “Warm the filtrate.”

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that of the Standard preparation as obtained in the Assay.

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C9H10N4O2S2 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 267 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Sulfamethizole RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C9H10N4O2S2 is dissolved in 30 minutes.

Mobile phase , Standard preparation, and Chromatographic system—Prepare as directed in the Assay under Sulfamethizole.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 40 mg of sulfamethizole, to a 250-mL screw-capped bottle. Transfer 100.0 mL of methanol to the bottle, cap the bottle, shake by mechanical means for 30 minutes, and filter. Quantitatively dilute a portion of the filtered solution with Mobile phase to obtain the Assay preparation having a concentration of about 8 µg per mL.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C9H10N4O2S2 in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Sulfamethizole RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.