Medium: 0.05MpH7.5phosphate buffer prepared by dissolving 6.8g of monobasic potassium phosphate and 1g of sodium hydroxide in water to make 1000mLof solution,and adjusting with 10Nsodium hydroxide to a pHof 7.50±0.05.

Apparatus 2: 100rpm.

Times: 1,2,4,and 8hours.

Procedure— Determine the amount of C7H7NO3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 330nm of filtered portions of the solution under test suitably diluted with Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Mesalamine RSin the same Medium.

Tolerances— The percentages of the labeled amount of C7H7NO3dissolved at the times specified conform to Acceptance Table 1.

Buffer— Dissolve 6.8g of monobasic potassium phosphate and 1.65g of sodium hydroxide in 800mLof water,adjust with 1Nsodium hydroxide to a pHof 7.5,dilute with water to 1000mL,and mix.

Mobile phase A— Dissolve 3.4g of tetrabutylammonium hydrogen sulfate and 1.4g of sodium acetate trihydrate in 1000mLof water,and adjust with 1Nsodium hydroxide to a pHof 6.6.Add 200mLof acetonitrile,mix,and filter through a filter having a porosity of 0.5µm or finer.Make any necessary adjustments (see System Suitabilityunder Chromatography á621ñ).[NOTE—Increasing the proportion of acetonitrile decreases the retention times.Prepare fresh daily.]

Mobile phase B— Dissolve 4.6g of tetrabutylammonium hydrogen sulfate and 1.9g of sodium acetate trihydrate in 1000mLof water,and adjust with 1Nsodium hydroxide to a pHof 6.6.Add 650mLof acetonitrile,mix,and filter through a filter having a porosity of 0.5µm or finer.Make any necessary adjustments (see System Suitabilityunder Chromatography á621ñ).[NOTE—Prepare fresh daily.]

Internal standard solution— Prepare a solution in Buffercontaining about 35mg of sodium benzoate per mL.

Standard preparation— Transfer about 50mg of USP Mesalamine RS,accurately weighed,to a 100-mLvolumetric flask,add 4.0mLof Internal standard solution,mix,dilute with Bufferto volume,and mix.Transfer 5.0mLof this solution to a 25-mLvolumetric flask,dilute with Bufferto volume,and mix.

Assay preparation— Transfer,as completely as possible,the contents of not less than 20Capsules to a suitable tared container,and determine the average weight of the contents of a Capsule.Finely powder the Capsule contents so that the powder thus obtained passes through a No.40sieve (see Powder Fineness á811ñ).Transfer an accurately weighed portion of the powder,equivalent to about 250mg of mesalamine,to a 500-mLvolumetric flask,add 20.0mLof Internal standard solutionand about 300mLof Buffer,and shake by mechanical means for 1hour.Dilute with Bufferto volume,and mix.Transfer 5.0mLof this solution to a 25-mLvolumetric flask,dilute with Bufferto volume,mix,and filter about 10mLof this solution through a 0.5-µm or finer porosity filter.Use the filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 240-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1,and is programmed to provide variable mixtures of Mobile phase Aand Mobile phase B.The flow rate is about 1.5mLper minute.The system is equilibrated with Mobile phase A.Five minutes after the injection of the Standard preparationand the Assay preparation,the proportion of Mobile Phase Bis increased linearly from 0%to 100%over a period of 2minutes,and held for 8minutes.The proportion of Mobile phase Ais then increased linearly from 0%to 100%over a period of 2minutes and held for 3minutes.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.6for mesalamine and 1.0for sodium benzoate,the resolution,R,between the mesalamine peak and the sodium benzoate 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 10µL)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 C7H7NO3in the portion of Capsule contents taken by the formula: in which Cis the concentration,in mg per mL,of USP Mesalamine RSin the Standard preparation;and RUand RSare the peak response ratios of the mesalamine peak to the sodium benzoate peak obtained from the Assay preparationand the Standard preparation,respectively.