A: Grind 1 Tablet to a fine powder in a mortar, add about 5 mL of chloroform, and swirl. Filter the mixture, and evaporate the filtrate with the aid of a stream of nitrogen to dryness: the IR absorption 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: pH 7.2 phosphate buffer (see under Buffers in the section Reagents, Indicators, and Solutions); 900 mL.

Apparatus 2: 50 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C13H18O2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 221 nm 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 RS in the same medium. [NOTE—Where the Tablets are labeled as gelatin-coated, determine the amount of C13H18O2 dissolved from the UV absorbance at the wavelength of maximum absorbance at about 266 nm from which is subtracted the absorbance at 280 nm, in comparison with the Standard solution similarly measured.]

Tolerances— Not less than 80% (Q) of the labeled amount of C13H18O2 is dissolved in 60 minutes.

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

(Official January 1, 2007)

Mobile phase, Internal standard solution, and Standard preparation— Prepare as directed in the Assay under 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 0.6 mg per mL. Add 2.0 mL of this stock solution to 100.0 mL of Internal standard solution, and mix to obtain a solution having a known concentration of about 0.012 mg of 4-isobutylacetophenone per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 1200 mg of ibuprofen, to a suitable container, add 100.0 mL of Internal standard solution, and shake for 10 minutes. [NOTE—Where the Tablets are coated, place an accurately counted number of Tablets, equivalent to not less than 1200 mg of ibuprofen, in a container, add an accurately measured volume of Internal standard solution, sufficient to obtain an Assay preparation containing about 12 mg of ibuprofen per mL, and about 15 glass 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 621)—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 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.75 for ibuprofen and 1.0 for 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 for Procedure: the relative retention times are about 1.0 for valerophenone and 1.2 for 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 5 µL) of the Standard preparation, the Assay preparation, and the 4-Isobutylacetophenone standard solution into 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 C is the concentration, in mg per mL, of USP Ibuprofen RS in the Standard preparation; A is the average weight, in mg, of a Tablet; W is the weight, in mg, of Tablet powder taken to prepare the Assay preparation; and RU and RS are the ratios of the ibuprofen peak response to the valerophenone peak response obtained from the Assay preparation and the Standard preparation, respectively, or where intact Tablets were taken, calculate the quantity, in mg, of C13H18O2 in each Tablet by the formula: in which V is the volume, in mL, of Internal standard solution used to prepare the Assay preparation; N is the number of Tablets taken; and the other terms are as defined above.