(Official January 1, 2007)

Acetate buffer— Dissolve 1.4 g of potassium acetate in 980 mL of water, adjust with about 2 mL of glacial acetic acid to a pH of 4.3 ± 0.1, dilute with water to 1000 mL, and mix. Adjust the buffer molarity (0.018-0.072 M) as necessary to obtain suitable chromatographic performance. Increased retention time may be achieved by a decrease in the buffer molarity.

Mobile phase— Prepare a filtered and degassed mixture of methanol and Acetate buffer (65:35). Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluent— Prepare a mixture of methanol and Acetate buffer (6:4).

Internal standard solution— Dissolve 1-benzylimidazole in methanol to obtain a solution containing about 1.6 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Butoconazole Nitrate RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a stock solution having a known concentration of about 400 µg per mL. Transfer 2.0 mL of this stock solution and 3.0 mL of Internal standard solution to a 50-mL flask, add 35.0 mL of Diluent, and mix.

Assay preparation— Place about 200 mL of methanol in a 250-mL volumetric flask. Transfer to the flask an accurately weighed quantity of Vaginal Cream, equivalent to about 100 mg of butoconazole nitrate, and sonicate until the Vaginal Cream is dissolved completely. Cool to room temperature, dilute with methanol to volume, and mix. Transfer 2.0 mL of this solution to a 50-mL flask, add 3.0 mL of Internal standard solution and 35.0 mL of Diluent, and mix. Allow the precipitated excipients which form to rise to the top of the solution, remove them by aspiration, and discard. Centrifuge or filter the remaining solution.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 225-nm detector and a 4.6-mm × 25-cm column that contains packing L9 which has been converted to the potassium form by the use of 0.555 M potassium acetate solution. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.6 for butoconazole nitrate and 1.0 for 1-benzylimidazole; the resolution, R, between the analyte and internal standard peaks is not less than 4.0; the column efficiency determined from the analyte peak is not less than 1100 theoretical plates; the tailing factor for the analyte peak is not more than 2.1; and the relative standard deviation for replicate injections is not more than 1.5%.

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. Calculate the quantity, in mg, of butoconazole nitrate (C19H17Cl3N2S·HNO3) in the portion of Vaginal Cream taken by the formula: in which C is the concentration, in µg per mL, of USP Butoconazole Nitrate RS in the stock solution used to prepare the Standard preparation; and RU and RS are the peak response ratios of butoconazole nitrate to the internal standard obtained from the Assay preparation and the Standard preparation, respectively.