A: Infrared Absorption 197M—[note—Do not dry or grind extensively.]

B: Ultraviolet Absorption 197U—

C: When moistened with hydrochloric acid, it meets the requirements of the flame test for Calcium 191.

Test solution: 50 mg per mL, in methanol.

0.1 M Ammonium acetate— Prepare as directed in the Assay.

Mobile phase— Prepare a filtered and degassed mixture of 0.1 M Ammonium acetate and tetrahydrofuran (70:30). Make adjustments if necessary (see System Suitability under Chromatography 621).

pH 4 Acetate buffer— Transfer about 13.6 g of sodium acetate to a 1000-mL volumetric flask, and dissolve in about 900 mL of water. Adjust with glacial acetic acid to a pH of 4.0, and dilute with water to volume.

Diluent— Prepare a mixture of pH 4 Acetate buffer and methanol (1:1).

Standard solution— Transfer about 25 mg of USP Mupirocin Lithium RS, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix.

Test solution— Transfer about 50 mg of Mupirocin Calcium, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix.

Resolution solution— Adjust 10 mL of the Standard solution with 6 N hydrochloric acid to a pH of 2.0, allow to stand for 20 hours, and adjust with 5 N sodium hydroxide to a pH of 4.0.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 240-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between the second of two peaks corresponding to hydrolysis products and the peak corresponding to mupirocin is not less than 7.0. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.75 (6 minutes) for pseudomonic acid D and 1.0 (14 minutes) for mupirocin; the column efficiency for the mupirocin peak is not less than 3000 theoretical plates; the tailing factor for the mupirocin peak is not more than 2; and the relative standard deviation of the mupirocin peak for replicate injections is not more than 5%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, and measure the peak area responses for all of the peaks. Calculate the percentage of each related compound in the portion of Mupirocin Calcium taken by the formula: in which E is the mupirocin equivalent, in µg per mg, of USP Mupirocin Lithium RS; WS is the weight, in mg, of USP Mupirocin Lithium RS taken to prepare the Standard solution; WU is the weight, in mg, of Mupirocin Calcium taken to prepare the Test solution; ri is the peak area for any impurity obtained from the Test solution; and rS is the peak area for mupirocin obtained from the Standard solution: the area of any peak corresponding to pseudomonic acid D is not greater than 2.5%; the area of any peak, excluding the mupirocin peak and any peak corresponding to pseudomonic acid D, is not greater than 1%; and the sum of the areas of all the peaks, excluding the principal peak, is not greater than 4.5%. Disregard any peak with an area less than 0.05 times the area of the mupirocin peak in the chromatogram obtained from the Standard solution.

0.1 M Ammonium acetate— Transfer about 7.7 g of ammonium acetate to a 1000-mL volumetric flask, dissolve in about 900 mL of water, adjust with glacial acetic acid to a pH of 5.7, and dilute with water to volume.

Mobile phase— Prepare a filtered and degassed mixture of 0.1 M Ammonium acetate and tetrahydrofuran (68:32). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 25 mg of USP Mupirocin Lithium RS, accurately weighed, to a 200-mL volumetric flask, dissolve in 5 mL of methanol, dilute with 0.1 M Ammonium acetate to volume, and mix.

Assay preparation— Transfer about 25 mg of Mupirocin Calcium, accurately weighed, to a 200-mL volumetric flask, dissolve in 5 mL of methanol, dilute with 0.1 M Ammonium acetate to volume, and mix.

Resolution solution— Adjust 10 mL of the Standard preparation with 6 N hydrochloric acid to a pH of 2.0, and allow to stand for 20 hours.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, of the second of the two peaks corresponding to hydrolysis products and the peak corresponding to mupirocin is not less than 7.0. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, and measure the peak area responses for the major peaks. Calculate the quantity, in µg, of mupirocin (C26H44O9) in each mg of Mupirocin Calcium taken by the formula: in which E is the designated mupirocin equivalent, in µg, of mupirocin in each mg of USP Mupirocin Lithium RS; MS is the weight, in mg, of USP Mupirocin Lithium RS taken to prepare the Standard preparation; MU is the weight, in mg, of Mupirocin Calcium taken to prepare the Assay preparation; and rU and rS are the mupirocin peak area responses obtained from the Assay preparation and the Standard preparation, respectively.