Add the following:

FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.USP28

Add the following:

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.USP28

Mobile phase— Prepare a mixture of 500mLof methanol,500mLof water,and 2.46g of anhydrous sodium acetate,and mix until dissolved.Adjust with glacial acetic acid to a pHof 5.8.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of ethylparaben in methanol containing about 1.1mg per mL.

Standard preparation— Transfer about 62.5mg of USP Naproxen RS,accurately weighed,to a 50-mLvolumetric flask,add about 30mLof methanol,and sonicate to dissolve.Add 5.0mLof Internal standard solution,dilute with methanol to volume,and mix.Transfer 2.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.This solution contains about 50µg of USP Naproxen RSand 4.4µg of ethylparaben per mL.

Assay preparation— Transfer an accurately measured volume of Oral Suspension,previously well-mixed and free from air bubbles,equivalent to about 125mg of naproxen,to a 100-mLvolumetric flask,using a “to contain”pipet.Rinse the pipet several times with methanol,and add the rinsings to the volumetric flask.Add 10.0mLof Internal standard solution,dilute with methanol to volume,and mix.Transfer 2.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Filter,if necessary,to obtain a clear solution.

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 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.6for ethylparaben and 1.0for naproxen;the resolution,R,between ethylparaben and naproxen is not less than 3.0;the tailing factor for the naproxen peak is not more than 2.0;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 35µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of naproxen (C14H14O3)in each mLof the Oral Suspension taken by the formula: in which Cis the concentration,in µg per mL,of USP Naproxen 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 response of the naproxen peak to the response of the ethylparaben peak obtained from the Assay preparationand the Standard preparation,respectively.