A: The RF values of the principal fluorescent spot and the principal blue spot in the chromatogram of the Test preparation correspond to those in the chromatogram of the Standard preparation, as obtained in the test for Related alkaloids under Ergonovine Maleate, using the Injection instead of Ergonovine Maleate.

B: Dilute a volume of Injection with water to obtain a solution having a concentration of about 0.67 mg per mL: the solution exhibits a bluish fluorescence under UV light. To this solution, add 2 mL of a solution of glacial acetic acid in ethyl acetate (1 in 2), and stratify 2 mL of sulfuric acid, by pipetting, under the solution: a bluish purple ring appears at the interface of the two liquids.

Solvent mixture— Mix 9 volumes of alcohol with 1 volume of ammonium hydroxide.

Test preparation— Transfer a volume of Injection, equivalent to about 5 mg of methylergonovine maleate, to a separator, and extract with three 5-mL portions of chloroform. Discard the chloroform extracts. Render alkaline to litmus with 6 N ammonium hydroxide, and extract with three 5-mL portions of chloroform. Evaporate the combined extracts with the aid of a current of air, but without heat, to dryness. Dissolve the residue so obtained in 0.5 mL of Solvent mixture.

Standard preparation and Standard dilutions— Prepare a solution of USP Methylergonovine Maleate RS in Solvent mixture to contain 10 mg per mL (Standard preparation). Prepare a series of dilutions of the Standard preparation in Solvent mixture to contain 0.50 mg, 0.20 mg, 0.10 mg, and 0.05 mg per mL (Standard dilutions).

Procedure— In a suitable chromatographic chamber arranged for thin-layer chromatography place a volume of a solvent system consisting of a mixture of chloroform, methanol, and water (75:25:3) sufficient to develop the chromatogram, cover, and allow to equilibrate for 30 minutes. Apply 5-µL portions of the Test preparation, the Standard preparation, and each of the three Standard dilutions to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Locate the spots on the plate by spraying thoroughly and evenly with a solution prepared by dissolving 1 g of p-dimethylaminobenzaldehyde in a cooled mixture of 50 mL of alcohol and 50 mL of hydrochloric acid: the RF value of the principal spot obtained from the Test preparation corresponds to that obtained from the Standard preparation. Estimate the concentration of any other spots observed in the lane for the Test preparation by comparison with the Standard dilutions: the spots from the 0.50-, 0.20-, 0.10-, and 0.05-mg-per-mL dilutions are equivalent to 5.0%, 2.0%, 1.0%, and 0.50% of impurities, respectively. The sum of the impurities is not greater than 5.0%.

Mobile phase— Prepare a filtered and degassed mixture of 800 mL of monobasic potassium phosphate solution (1 in 500) and 200 mL of acetonitrile. Make adjustments if necessary (see System Suitability under Chromatography 621).

Extraction solvent— Dissolve 5 g of tartaric acid in 500 mL of water. Add 500 mL of methanol, and mix.

Standard preparation— Transfer about 20 mg of USP Methylergonovine Maleate RS, accurately weighed, to a 200-mL volumetric flask. Add 150 mL of Extraction solvent, and shake by mechanical means for 15 minutes. Dilute with the Extraction solvent to volume, and mix to obtain the Standard preparation having a known concentration of about 100 µg of USP Methylergonovine Maleate RS per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 10 mg of methylergonovine maleate to a 100-mL volumetric flask. Dilute with Extraction solvent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 240-nm detector, and a 4-mm × 25-cm column that contains packing L7 maintained at 30. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency determined from the analyte peak is not less than 1000 theoretical plates, the tailing factor is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of methylergonovine maleate (C20H25N3O2·C4H4O4) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Methylergonovine Maleate RS in the Standard preparation; V is the volume, in mL, of Injection taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.