Test solution: 10 mg per mL, in dimethylformamide.

Solution A— Prepare a filtered and degassed mixture of 5.0 mL of morpholine with 995 mL of water, and adjust with phosphoric acid to a pH of 7.0.

Solution B— Prepare a filtered and degassed mixture of methanol, acetonitrile, and tetrahydrofuran (1:1:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system (see System Suitability under Chromatography 621).

Standard solution 1— Dissolve an accurately weighed quantity of USP Pergolide Mesylate RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 30 µg per mL.

Standard solution 2— Dilute 10.0 mL of Standard solution 1 to 50 mL with methanol.

Test solution— Transfer about 60 mg of Pergolide Mesylate, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 25-cm column that contains base-deactivated packing L1. The flow rate is about 1 mL per minute. The column temperature is maintained at 40. The chromatograph is programmed as follows. Chromatograph Standard solution 1, and record the peak responses as directed for Procedure: the column efficiency is not less than 10,000 theoretical plates; the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of Standard solution 1, Standard solution 2, the Test solution, and a methanol blank into the chromatograph, record the chromatograms, and measure all of the peak responses. Disregard the contributions due to any peaks found in the methanol blank. The sum of the peak responses, excluding that of pergolide, from the Test solution is not more than the pergolide peak response obtained from Standard solution 1 (0.5%), and no single peak response is more than the pergolide peak response obtained from Standard solution 2 (0.1%).

Diluent— Dissolve 5 mg of methionine in 500 mL of 0.01 N hydrochloric acid. Add 500 mL of methanol, and mix.

Mobile phase— Prepare a solution of 0.009 M sodium 1-octanesulfonate containing 1.0 mL of glacial acetic acid per L. Prepare a filtered and degassed mixture of this solution, methanol, and acetonitrile (2:1:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Dissolve about 4 mg of USP Pergolide Sulfoxide RS and 8 mg of USP Pergolide Mesylate RS in 50 mL of Diluent.

Standard preparation— Dissolve an accurately weighed quantity of USP Pergolide Mesylate RS in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 0.13 mg per mL.

Assay preparation— Transfer about 6.5 mg of Pergolide Mesylate, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 25-cm column that contains base-deactivated packing L7. The flow rate is about 1 mL per minute. The column temperature is maintained at 40. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between pergolide sulfoxide and pergolide is not less than 12.0. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the pergolide peaks. Calculate the quantity, in mg, of C19H26N2S·CH4O3S in the portion of Pergolide Mesylate taken by the formula: in which C is the concentration, in mg per mL, of USP Pergolide Mesylate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.