(meth'' il doe' pate hye'' droe klor' ide).
l-Tyrosine, 3-hydroxy--methyl-, ethyl ester, hydrochloride.
l-3-(3,4-Dihydroxyphenyl)-2-methylalanine ethyl ester hydrochloride [5123-53-5; 2508-79-4].
» Methyldopate Hydrochloride contains not less than 98.0 percent and not more than 101.0 percent of C12H17NO4·HCl, calculated on the dried basis.
Packaging and storage Preserve in well-closed containers. Store at 25, excursions permitted between 15 and 30.
USP Reference standards 11
B: Ultraviolet Absorption 197U
Solution: 50 µg per mL.
Medium: 0.1 N hydrochloric acid.
Absorptivities at 280 nm, calculated on the dried basis, do not differ by more than 3.0%.
C: It responds to Identification test C under Methyldopa.
D: It responds to the tests for Chloride 191, except that on the addition of the slight excess of 6 N ammonium hydroxide a brown precipitate is formed.
Specific rotation 781S: between 13.5 and 14.9 ( = 405 nm).
Test solution: 40 mg per mL, in 0.1 N hydrochloric acid.
pH 791: between 3.0 and 5.0, in a solution (1 in 100).
Loss on drying 731 Dry it at 100 and at a pressure not exceeding 5 mm of mercury for 2 hours: it loses not more than 0.5% of its weight.
Residue on ignition 281: not more than 0.1%.
Heavy metals, Method II 231: 0.001%.
Mobile solvent Prepare a suitable solution of 0.02 M monobasic sodium phosphate and 0.015 M phosphoric acid in a water and methanol solution (approximately 15.5:4.5) such that the retention time of methyldopate hydrochloride is approximately 6.5 minutes.
Standard preparation Dissolve an accurately weighed quantity of USP Methyldopate Hydrochloride RS in the Mobile solvent to obtain a solution containing about 1 mg per mL.
Assay preparation Transfer about 50 mg of Methyldopate Hydrochloride, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Mobile solvent to volume.
Procedure Introduce separately 20-µL portions of the Assay preparation and the Standard preparation into a high-pressure liquid chromatograph (see Chromatography 621) operated at 25, by means of a suitable microsyringe or sampling valve, adjusting the operating parameters such that the peak obtained with the Standard preparation is 100% full-scale. Typically, the apparatus is fitted with a 4-mm × 30-cm column that contains packing L1, is equipped with an UV detector capable of monitoring absorption at 280 nm and a suitable recorder, and is capable of operating at a column pressure between 700 and 1700 psi. In a suitable chromatogram, three replicate injections of the Standard preparation show a relative standard deviation of not more than 1.5%. Determine the peak areas, at equivalent retention times, obtained with the Assay preparation and the Standard preparation, and calculate the quantity, in mg, of C12H17NO4·HCl in the portion of Methyldopate Hydrochloride taken by the formula:
50C(AU / AS)in which C is the concentration, in mg per mL, of USP Methyldopate Hydrochloride RS in the Standard preparation; and AU and AS are the peak areas obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 3874Pharmacopeial Forum: Volume No. 29(5) Page 1534