A: To 10 mL of a 1 in 10,000 solution in sodium hydroxide solution (1 in 2500) add 0.1 mL of hydrochloric acid: it exhibits absorption maxima at 295 ± 2 nm and at 286 ± 2 nm. The ratio A295 / A286 is between 0.90 and 1.00.

B: Infrared Absorption 197M.

Mobile solvent— Prepare a suitable solution of 0.02 M monobasic sodium phosphate and 0.02 M dibasic sodium phosphate in acetonitrile and water (approximately 1:1) such that the retention time of Dichlorphenamide is approximately 6 minutes.

Standard preparation— Dissolve an accurately weighed quantity of USP Dichlorphenamide RS in Mobile solvent to obtain a solution containing about 1 mg per mL.

Assay preparation— Accurately weigh about 50 mg of Dichlorphenamide, and prepare as directed for Standard preparation.

Procedure— Introduce separately 20-µL portions of the Assay preparation and the Standard preparation into a high-pressure liquid chromatograph (see Chromatography 621) operated at 25, by means of a suitable microsyringe or sampling valve, adjusting the operating parameters such that the peak obtained with the Standard preparation is full-scale. Typically, the apparatus is fitted with a 4-mm × 30-cm column, packed with packing L1, is equipped with an UV detector capable of monitoring absorption at 280 nm and a suitable recorder, and is capable of operating at a column pressure of up to 3500 psi. Five replicate injections of the Standard preparation show a relative standard deviation of not more than 1.5%. Calculate the quantity, in mg, of C6H6Cl2N2O4S2 in the portion of Dichlorphenamide taken by the formula: in which C is the concentration, in mg per mL, of USP Dichlorphenamide RS in the Standard preparation; and AU and AS are the area responses obtained at equivalent retention times from the Assay preparation and the Standard preparation, respectively.