FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

(Official January 1, 2007)

Mobile phase— Prepare a solution of 784 mg of dibasic potassium phosphate in 325 mL of water. To this solution add a solution of 2.62 g of hexadecyltrimethylammonium bromide in 350 mL of methanol. To the combined solution add 325 mL of methanol, mix, filter, and degas. This solution has an apparent pH of about 10. Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Prepare a solution of sulfanilic acid in Mobile phase containing about 0.8 mg per mL.

Standard preparation— Prepare a solution having a known concentration of about 0.18 mg per mL of USP Nalidixic Acid RS in methanol. Transfer 5.0 mL of this solution and 1.0 mL of Internal standard solution to a 25-mL volumetric flask, dilute with methanol to volume, and mix.

Assay preparation— Transfer an accurately measured volume of freshly mixed Oral Suspension, equivalent to about 150 mg of nalidixic acid, to a 500-mL volumetric flask, add about 400 mL of methanol, and sonicate for about 30 minutes. Shake by mechanical means for about 30 minutes, sonicate again for about 30 minutes, dilute with methanol to volume, mix, and filter. Transfer 3.0 mL of the clear filtrate and 1.0 mL of Internal standard solution to a 25-mL volumetric flask, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.7 for sulfanilic acid and 1.0 for nalidixic acid; the resolution, R, between sulfanilic acid and nalidixic acid is not less than 1; and the relative standard deviation for replicate injections is not more than 2.0%.

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 areas for the major peaks. Calculate the quantity, in mg, of nalidixic acid (C12H12N2O3) in each mL of the Oral Suspension taken by the formula: in which C is the concentration, in mg per mL, of USP Nalidixic Acid RS in the Standard preparation; V is the volume, in mL, of Oral Suspension taken to prepare the Assay preparation; and RU and RS are the ratios of the peak areas for nalidixic acid and sulfanilic acid in the chromatograms obtained from the Assay preparation and the Standard preparation, respectively.