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

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

Mobile phase— Prepare a solution of 784mg of dibasic potassium phosphate in 325mLof water.To this solution add a solution of 2.62g of hexadecyltrimethylammonium bromide in 350mLof methanol.To the combined solution add 325mLof methanol,mix,filter,and degas.This solution has an apparent pHof about 10.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

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

Chromatographic system(see Chromatography á621ñ)— 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 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for sulfanilic acid and 1.0for 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 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of nalidixic acid (C12H12N2O3)in each mLof the Oral Suspension taken by the formula: in which Cis the concentration,in mg per mL,of USP Nalidixic Acid RSin the Standard preparation;Vis the volume,in mL,of Oral Suspension taken to prepare the Assay preparation;and RUand RSare the ratios of the peak areas for nalidixic acid and sulfanilic acid in the chromatograms obtained from the Assay preparationand the Standard preparation,respectively.