(Official January 1, 2007)

Mobile phase and Chromatographic system—Proceed as directed in the Assay under Sulfaquinoxaline.

Standard preparation— Dissolve an accurately weighed quantity of USP Sulfaquinoxaline RS in 0.01 N sodium hydroxide to obtain a solution having a known concentration of about 0.7 mg per mL. Dilute an accurately measured volume of this solution quantitatively with water to obtain a solution having a known concentration of about 0.15 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 300 mg of sulfaquinoxaline, to a 2000-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Separately inject equal volumes (about 8 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 sulfaquinoxaline (C14H12N4O2S) in each mL of the Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Sulfaquinoxaline RS in the Standard preparation, V is the volume, in mL, of Oral Solution taken to prepare the Assay preparation, and rU and rS are the sulfaquinoxaline peak responses obtained from the Assay preparation and the Standard preparation, respectively.