Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C4H6N4O3S2 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 265 nm on filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Acetazolamide RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C4H6N4O3S2 is dissolved in 60 minutes.

(Official January 1, 2007)

Mobile phase— Dissolve 4.1 g of anhydrous sodium acetate in 950 mL of water, add 20 mL of methanol and 30 mL of acetonitrile, and mix. Adjust with glacial acetic acid to a pH of 4.0 ± 0.05. Filter and degas the solution. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard acetazolamide stock solution— Transfer about 25 mg of USP Acetazolamide RS, accurately weighed, to a 25-mL volumetric flask, add 2.5 mL of 0.5 N sodium hydroxide, and mix to dissolve. Dilute with water to volume, and mix.

Internal standard solution— Transfer about 100 mg of sulfadiazine to a 100-mL volumetric flask, add 10 mL of 0.5 N sodium hydroxide, and mix to dissolve. Dilute with water to volume, and mix.

Standard preparation— Transfer 10.0 mL of Standard acetazolamide stock solution and 10.0 mL of Internal standard solution to a 100-mL volumetric flask, add 10 mL of 0.5 N sodium hydroxide, dilute with water to volume, and mix to obtain a solution having a known concentration of about 0.1 mg of USP Acetazolamide RS per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of acetazolamide, to a 100-mL volumetric flask, add 10 mL of 0.5 N sodium hydroxide, and sonicate for 5 minutes. Cool to room temperature, dilute with water to volume, and mix. Filter a portion of this solution, discarding the first 20 mL of the filtrate. Transfer 10.0 mL of the clear filtrate to a 100-mL volumetric flask, add 10.0 mL of Internal standard solution and 10 mL of 0.5 N sodium hydroxide, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 2.0; and the relative standard deviation of the ratios of the analyte peak response to the internal standard peak response for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.7 for acetazolamide and 1.0 for sulfadiazine. Calculate the quantity, in mg, of acetazolamide (C4H6N4O3S2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Acetazolamide RS in the Standard preparation; and RU and RS are the peak response ratios of the analyte peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.