0.1M ,pH7.4phosphate buffer—Dissolve 2.62g of monobasic sodium phosphate and 11.50g of anhydrous dibasic sodium phosphate in 1000mLof water,and mix.

Medium: 0.1M,pH7.4phosphate buffer;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C14H14O3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 332nm of filtered portions of the solution under test,suitably diluted with 0.1M,pH7.4phosphate buffer,in comparison with a Standard solution having a known concentration of USP Naproxen RSin the same medium.

Tolerances— Not less than 80%(Q)of the labeled amount of C14H14O3is dissolved in 45minutes.

Mobile phase— Prepare a suitable mixture of acetonitrile,water,and glacial acetic acid (50:49:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Increased resolution may be achieved by increasing the proportion of water in the Mobile phase.

Solvent mixture— Prepare a suitable mixture of acetonitrile and water (90:10).

Internal standard solution— Dilute 5mLof butyrophenone with acetonitrile to make 100mL.Dilute 1mLof the resulting solution with acetonitrile to make 100mL.Each mLof this solution contains about 0.5µLof butyrophenone.

Standard preparation— Dissolve an accurately weighed quantity of USP Naproxen RSin Solvent mixtureto obtain a solution having a known concentration of about 2.5mg per mL.Transfer 1.0mLof the resulting solution and 2.0mLof Internal standard solutionto a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.This solution contains about 25µg of USP Naproxen RSper mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed quantity of the powder,equivalent to about 250mg of naproxen,to a 100-mLvolumetric flask.Add 10mLof water,and sonicate for 10minutes until the material is completely dispersed.Add about 80mLof acetonitrile,and sonicate for an additional 5minutes.Allow the flask to reach room temperature,dilute with acetonitrile to volume,and mix.Allow any insoluble matter to settle,then transfer 1.0mLof the clear supernatant to a 100-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L1.The flow rate is about 1.2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the column efficiency,determined from the analyte peak,is not less than 4000theoretical plates when calculated by the formula: the resolution between the analyte and internal standard peaks is not less than 11.5when calculated by the formula: and the relative standard deviation of replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.6for naproxen and 1.0for the internal standard.Calculate the quantity,in mg,of C14H14O3in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Naproxen RSin the Standard preparation,and RUand RSare the ratios of the response of the naproxen peak to the response of the internal standard peak obtained from the Assay preparationand the Standard preparation,respectively.