Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C9H11NO4 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 280 nm on filtered portions of the solution under test, suitably diluted with Medium, in comparison with a Standard solution having a known concentration of USP Levodopa RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C9H11NO4 is dissolved in 30 minutes.

Mobile phase, System suitability solution, and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Use the Standard preparation, prepared as directed in the Assay.

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak areas. Calculate the percentage of each impurity in the portion of Tablets taken by the formula: in which F is the relative response factor of the impurity according to the table below; WT is the average weight, in mg, of the Tablets; WS is the weight, in mg, of sample taken to prepare the Test solution; C is the concentration, in mg per mL, of USP Levodopa RS in the Standard solution; D is the labeled amount, in mg, of levodopa per tablet; ri is the peak area for any impurity in the Test solution; and rS is the peak area for levodopa in the Standard solution: the impurities meet the requirements given in the table below.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed solution of 0.01 M monobasic potassium phosphate, adjust with a mixture of phosphoric acid and acetonitrile (97:3) to a pH of 2.0, and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Dissolve suitable quantities of USP Levodopa RS, USP 3-Methoxytyrosine RS, and USP Levodopa Related Compound A RS in Mobile phase to obtain a solution containing about 10 µg of each per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Levodopa RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.4 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 40 mg of levodopa, to a 100-mL volumetric flask, add 50 mL of Mobile phase, sonicate for about 5 minutes, cool to room temperature, dilute with Mobile phase to volume, and filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 3.0-mm × 25-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.7 for levodopa related compound A, 1.0 for levodopa, and 2.8 for 3-methoxytyrosine; the resolution, R, between levodopa and levodopa related compound A is not less than 3.5; and the relative standard deviation for levodopa 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 per mL, of levodopa (C9H11NO4) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Levodopa RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.