»Levodopa Tablets contain not less than 90.0percent and not more than 110.0percent of the labeled amount of levodopa (C9H11NO4).
Packaging and storage Preserve in tight,light-resistant containers,in a dry place,and prevent exposure to excessive heat.
USP Reference standards á11ñ USP Levodopa RS.USP Levodopa Related Compound A RS.USP3-Methoxytyrosine RS.
Identification Shake a quantity of powdered Tablets,equivalent to about 500mg of levodopa,with 25mLof 3Nhydrochloric acid,and filter.Adjust the acidity of the filtrate with 6Nammonium hydroxide,added dropwise with stirring,and allow to stand,protected from light,for several hours.Filter,wash the precipitate with water,and dry at 105:the residue meets the requirements for Identificationtest Aunder Levodopa.
Medium: 0.01Nhydrochloric acid;900mL.
Apparatus 1: 100rpm.
Procedure Determine the amount of C9H11NO4dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 280nm on filtered portions of the solution under test,suitably diluted with Dissolution Medium,in comparison with a Standard solution having a known concentration of USP Levodopa RSin the same Medium.
Tolerances Not less than 75%(Q)of the labeled amount of C9H11NO4is dissolved in 30minutes.
Uniformity of dosage units á905ñ: meet the requirements.
Related compounds [NOTEProtect all solutions from light and maintain them at 10until they are injected into the chromatograph.]
Mobile phase,System suitability solution,andChromatographic system Proceed as directed in the Assay.
Standard solution Prepare as directed for the Standard preparationin the Assay.
Test solution Use the Assay preparation.
Procedure Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity in the portion of Tablets taken by the formula:
100(ri/rs),in which riis the peak response for each impurity obtained from the Test solution;and rsis the sum of the responses of all the peaks:not more than 0.1%of levodopa related compound Ais found;not more than 0.5%of 3-methoxytyrosine is found;not more than 0.1%of any other individual impurity is found;and the sum of all unknown impurities is not more than 0.3%.
Assay [NOTEProtect all solutions from light and maintain them at 10until they are injected into the chromatograph.]
Mobile phase Prepare a filtered and degassed solution of 0.01Mmonobasic potassium phosphate,adjust with a mixture of phosphoric acid and acetonitrile (97:3)to a pHof 2.0,and mix.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).
System suitability solution Dissolve suitable quantities of USP Levodopa RS,USP3-Methoxytyrosine RS,and USP Levodopa Related Compound A RSin Mobile phaseto obtain a solution containing about 10µg of each per mL.
Standard preparation Dissolve an accurately weighed quantity of USP Levodopa RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.4mg per mL.
Assay preparation Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 40mg of levodopa,to a 100-mLvolumetric flask,add 50mLof Mobile phase,sonicate for about 5minutes,cool to room temperature,dilute with Mobile phaseto volume,and filter.
Chromatographic system (see Chromatography á621ñ) 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 1.0mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for levodopa related compound A,1.0for levodopa,and 2.8for 3-methoxytyrosine;the resolution,R,between levodopa and levodopa related compound Ais 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 20µL)of the Standard preparationand the Assay preparationinto 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:
100C(rU/rS),in which Cis the concentration,in mg per mL,of USP Levodopa RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.
Auxiliary Information Staff Liaison:Salvador C.Salado,M.S.,Scientist and Latin American Liaison
Expert Committee:(PA3)Pharmaceutical Analysis 3
USP28NF23Page 1123Pharmacopeial Forum:Volume No.30(3)Page 890