Solution: 12 µg per mL.

Medium: 0.1 N hydrochloric acid.

Mobile phase— Dissolve 1.36 g of monobasic potassium phosphate and 2.2 g of sodium 1-octanesulfonate in 890 mL of water, and adjust with phosphoric acid to a pH of 2.2. Pass through a filter having a 0.5-µm or finer porosity. To the filtrate add 80 mL of methanol and 30 mL of acetonitrile. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Quantitatively dissolve accurately weighed quantities of USP Mesalamine RS and 3-aminosalicylic acid in Mobile phase to obtain a solution having known concentrations of about 1 µg of each per mL.

Test solution— Transfer about 50 mg of Mesalamine, accurately weighed, to a 100-mL volumetric flask, add about 75 mL of Mobile phase, and sonicate briefly to dissolve. Dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L7. The flow rate is about 1.2 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative retention times are about 1.0 for mesalamine and 1.3 for 3-aminosalicylic acid; and the resolution, R, between mesalamine and 3-aminosalicylic acid is not less than 2.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms for a period of time that is three times the retention time of mesalamine, and measure the peak area responses. Calculate the percentage of 3-aminosalicylic acid by the formula: in which C3 is the concentration, in µg per mL, of 3-aminosalicylic acid in the Standard solution; r3 is the response of the 3-aminosalicylic acid peak in the chromatogram obtained from the Test solution; and rS3 is the response of the 3-aminosalicylic acid peak in the chromatogram obtained from the Standard solution. Calculate the percentage of each other impurity by the formula: in which Cm is the concentration, in µg per mL, of USP Mesalamine RS in the Standard solution; ri is the response of the individual impurity peak in the chromatogram obtained from the Test solution; and rSm is the response of the mesalamine peak in the chromatogram obtained from the Standard solution: not more than 0.2% of 3-aminosalicylic acid is found; not more than 0.2% of any other impurity, expressed in terms of mesalamine equivalent, is found; and the total of all impurities found is not more than 1.0%.

Standard solution— Prepare a solution of aniline, 2-aminophenol, and 4-aminophenol in methanol having concentrations of 0.05, 2, and 2 mg per mL, respectively; and dilute quantitatively, and stepwise if necessary, with methylene chloride to obtain a solution having concentrations of 0.5, 20, and 20 µg per mL, respectively.

Test solution— Mix 1.0 g of Mesalamine with 10.0 mL of methylene chloride. Allow to settle, and use the clear methylene chloride solution as the Test solution.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.53-mm × 10-m fused-silica capillary column coated with a 2.65-µm film of stationary phase G27. The carrier gas is helium flowing at a rate of 15 mL per minute. The injection port and the detector temperatures are maintained at about 280 and 300, respectively. The column temperature is programmed according to the following steps: the starting column temperature is 70; after injection it is held at 70 for 2 minutes, then increased to 150 at a rate of 30 per minute, then held for 1 minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.5 for aniline, 0.9 for 2-aminophenol, and 1.0 for 4-aminophenol; and the peaks are baseline separated.

Procedure— Separately inject equal volumes (about 2 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak area responses. Identify by retention time any peaks present in the chromatogram of the Test solution that correspond to those in the chromatogram obtained from the Standard solution. Calculate the quantities, in µg per g, of aniline, 2-aminophenol, and 4-aminophenol in the portion of Mesalamine taken by the formula: in which C is the concentration, in µg per mL, of the relevant analyte in the Standard solution; ra is the response of the relevant analyte in the chromatogram obtained from the Test solution; and rSa is the response of the relevant analyte in the chromatogram obtained from the Standard solution: not more than 5 µg of aniline, 200 µg of 2-aminophenol, and 200 µg of 4-aminophenol per g are found.

125C(rU / rS)