A: Grind 1Tablet to a fine powder in a mortar,add about 5mLof chloroform,and swirl.Filter the mixture,and evaporate the filtrate with the aid of a stream of nitrogen to dryness:the IRabsorption spectrum of a mineral oil dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Ibuprofen RS.

B: Its retention time,relative to that of the internal standard,determined as directed in the Assay,corresponds to that of USP Ibuprofen RS.

Medium: pH7.2phosphate buffer (see under Buffersin the section Reagents,Indicators,and Solutions);900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Procedure— Determine the amount of C13H18O2dissolved from UVabsorbances at the wavelength of maximum absorbance at about 221nm 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 Ibuprofen RSin the same medium.[NOTE—Where the Tablets are labeled as gelatin-coated,determine the amount of C13H18O2dissolved from the UVabsorbance at the wavelength of maximum absorbance at about 266nm from which is subtracted the absorbance at 280nm,in comparison with the Standard solution similarly measured.]

Tolerances— Not less than 80%(Q)of the labeled amount of C13H18O2is dissolved in 60minutes.

10,000C(A/WI)(RU/RS),

Mobile phase,Internal standard solution,and Standard preparation— Prepare as directed in the Assayunder Ibuprofen.

4-Isobutylacetophenone standard solution— Quantitatively dissolve an accurately weighed quantity of 4-isobutylacetophenone in acetonitrile to obtain a solution having a known concentration of about 0.6mg per mL.Add 2.0mLof this stock solution to 100.0mLof Internal standard solution,and mix to obtain a solution having a known concentration of about 0.012mg of 4-isobutylacetophenone per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 1200mg of ibuprofen,to a suitable container,add 100.0mLof Internal standard solution,and shake for 10minutes.[NOTE—Where the Tablets are coated,place an accurately counted number of Tablets,equivalent to not less than 1200mg of ibuprofen,in a container,add an accurately measured volume of Internal standard solution,sufficient to obtain an Assay preparation containing about 12mg of ibuprofen per mL,and about 15glass beads,and shake until the Tablets are completely disintegrated.]Centrifuge a portion of the suspension so obtained and use the clear supernatant as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative retention times are about 0.75for ibuprofen and 1.0for valerophenone,the tailing factors for the individual peaks are not more than 2.5,the resolution,R,between the ibuprofen peak and the valerophenone peak is not less than 2.5,and the relative standard deviation for replicate injections is not more than 2.0%.Chromatograph the 4-Isobutylacetophenone standard solution,and record the peak responses as directed under Procedure:the relative retention times are about 1.0for valerophenone and 1.2for 4-isobutylacetophenone,the tailing factors for the individual peaks are not more than 2.5,the resolution,R,between the valerophenone peak and the 4-isobutylacetophenone peak is not less than 2.5,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 5µL)of the Standard preparation,the Assay preparation,and the 4-Isobutylacetophenone standard solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of ibuprofen (C13H18O2)in each Tablet taken by the formula: in which Cis the concentration,in mg per mL,of USP Ibuprofen RSin the Standard preparation,Ais the average weight,in mg,of a Tablet,Wis the weight,in mg,of Tablet powder taken to prepare the Assay preparation,and RUand RSare the ratios of the ibuprofen peak response to the valerophenone peak response obtained from the Assay preparationand the Standard preparation,respectively,or where intact Tablets were taken,calculate the quantity,in mg,of C13H18O2in each Tablet by the formula: in which Vis the volume,in mL,of Internal standard solutionused to prepare the Assay preparation,Nis the number of Tablets taken,and the other terms are as defined above.