Medium: 0.05Macetate buffer,prepared by mixing 2.99g of sodium acetate trihydrate and 1.66mLof glacial acetic acid with water to obtain 1000mLof solution having a pHof 4.50±0.05;500mL.

Apparatus 1: 50rpm.

Time: 30minutes.

Procedure— Determine the amount of C18H21NO4dissolved using the method for Assay for oxycodone,making any necessary volumetric adjustments.Determine the amount of C9H8O4dissolved from UVabsorbances at the wavelength of the isobestic point of aspirin and salicylic acid at about 265nm of filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Aspirin RSin the same medium.[NOTE—Prepare the Standard solution at the time of use.An amount of alcohol not to exceed 1%of the total volume of the Standard solution may be used to bring the Reference Standard into solution prior to dilution with Dissolution Medium.]

Tolerances— Not less than 80%(Q)of the labeled amount of C18H21NO4is dissolved in 30minutes and not less than 75%(Q)of the labeled amount of C9H8O4is dissolved in 30minutes.

Mobile phase— Dissolve 2g of sodium 1-heptanesulfonate in a mixture of 850mLof water and 150mLof acetonitrile,and adjust with glacial acetic acid to a pHof 3.4.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a mixture of acetonitrile and formic acid (99:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Salicylic Acid RSin Diluting solutionto obtain a solution having a known concentration of about 0.008mg per mL.

Test preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed quantity of the powder,equivalent to about 380mg of aspirin,to a 100-mLvolumetric flask,add about 20mLof Diluting solution,and sonicate for about 15minutes.Dilute with Diluting solutionto volume,and mix.Centrifuge a portion of this mixture,and use the clear supernatant as the Test preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 299-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 responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 4.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Test preparationand the Standard preparationinto the chromatograph,record the chromatograms,and measure the responses for the salicylic acid peaks.Calculate the percentage of salicylic acid in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Salicylic Acid RSin the Standard preparation,ais the quantity,in mg,of aspirin in the portion of Tablets taken,as determined in the Assay for aspirin,and rUand rSare the salicylic acid peak responses obtained from the Test preparationand the Standard preparation,respectively:not more than 3.0%is found.

Mobile phase— Prepare a mixture of n-heptane and glacial acetic acid (96:4),and filter through a filter of 0.5µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare solution of 1-naphthol in chloroform containing about 1mg per mL.[NOTE—Protect this solution from light.]

Standard preparation— Transfer about 163mg of USP Aspirin RS,accurately weighed,to a 50-mLvolumetric flask.Add 2.5mLof glacial acetic acid,and swirl.Add 25mLof chloroform,and shake for 10minutes.Add 5.0mLof Internal standard solution,dilute with chloroform to volume,and mix.[NOTE—Protect this solution from light.]

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 325mg of aspirin,to a 100-mLvolumetric flask,add 5mLof glacial acetic acid,and swirl.Add 50mLof chloroform,and shake for 10minutes.Add 10.0mLof the Internal standard solution,dilute with chloroform to volume,mix,and filter.[NOTE—Prepare the Assay preparation and the Standard preparation concomitantly,and protect from light.]

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 300-nm detector and a 4.6-mm ×25-cm column containing packing L3.The flow rate is about 4mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between the 1-naphthol peak and the aspirin peak is not less than 2.0,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]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 0.65for 1-naphthol and 1.0for aspirin.Calculate the quantity,in mg,of Aspirin (C9H8O4)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Aspirin RSin the Standard preparation,and RUand RSare the ratios of the aspirin peak response to the 1-naphthol peak response obtained from the Assay preparationand the Standard preparation,respectively.

Mobile phase— Dissolve 2.2g of sodium 1-octanesulfonate in 740mLof water,add 260mLof methanol,10mLof glacial acetic acid,and 0.1mLof triethylamine.Mix,and adjust with 5Nsodium hydroxide to a pHof 6.5±0.1.Filter through a suitable filter of 0.5µm or finer porosity,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Use 0.1Nhydrochloric acid.

Internal standard solution— Transfer about 50mg of ethylparaben to a 500-mLvolumetric flask,add 10mLof methanol,and swirl to dissolve.Dilute with Diluting solutionto volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Oxycodone RSin Diluting solution,and dilute quantitatively with Diluting solutionto obtain a stock solution having a known concentration of about 0.75mg per mL.Transfer 15.0mLof this stock solution to a second 100-mLvolumetric flask,add 20.0mLof Internal standard solution,dilute with Diluting solutionto volume,and mix to obtain a Standard preparationhaving a known concentration of about 0.112mg of USP Oxycodone RSper mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 11.2mg of oxycodone,to a suitable glass-stoppered conical flask,add 50.0mLof Diluting solution,and shake by mechanical means for about 30minutes.Filter this solution,transfer 25.0mLof the clear filtrate to a 50-mLvolumetric flask,add 10.0mLof Internal standard solution,dilute with Diluting solutionto volume,and mix.Use this solution as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 280-nm detector and a 3.9-mm ×15-cm column that contains packing L1and is maintained at a temperature of 50±1.0.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the column efficiency,determined from the oxycodone peak,is not less than 1800theoretical plates,the resolution,R,between the oxycodone and the ethylparaben peaks is not less than 6,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 30µL)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 0.5for oxycodone and 1.0for ethylparaben.Calculate the quantity,in mg,of oxycodone (C18H21NO4)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Oxycodone RSin the Standard preparation,and RUand RSare the ratios of the responses of the oxycodone peak and the ethylparaben peak obtained from the Assay preparationand the Standard preparation,respectively.