A: To about 10mg of finely ground Tablets add 3drops of a solution of ninhydrin in sulfuric acid (1in 250):a dark purple color is produced within 5to 10minutes.Add 3drops of water:the color changes to pale brownish yellow.

B: To about 10mg of finely ground Tablets add 2mLof 0.1Nsulfuric acid and 2mLof Ferrous tartrate solutionprepared as directed in the Assay,then add 0.25mLof 6Nammonium hydroxide,and mix:a dark purple color is produced immediately.

Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 20minutes.

Procedure— Determine the amount of C10H13NO4dissolved from UVabsorbances at the wavelength of maximum absorbance at about 280nm of filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Methyldopa RSin the same medium.

Tolerances— Not less than 80%(Q)of the labeled amount of C10H13NO4is dissolved in 20minutes.

Ferrous tartrate solution— Dissolve 1g of ferrous sulfate,2g of potassium sodium tartrate,and 100mg of sodium bisulfite in water to make 100mL.Prepare this solution fresh.

Buffer solution— Dissolve 50g of ammonium acetate in 1000mLof 20percent alcohol.Adjust with 6Nammonium hydroxide to a pHof 8.5.

Standard preparation— Dissolve a suitable quantity of USP Methyldopa RSin 0.1Nsulfuric acid to obtain a solution having a known concentration of about 1mg of anhydrous methyldopa per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of methyldopa,to a 100-mLvolumetric flask,add 50mLof 0.1Nsulfuric acid,agitate by mechanical means for 15minutes,add the dilute acid to volume,and mix.Filter the solution,rejecting the first 20mLof the filtrate.

Procedure— Pipet 5mLeach of the Assay preparationand the Standard preparationinto separate 100-mLvolumetric flasks.To a third 100-mLvolumetric flask add 5mLof water to provide a blank.Add to each flask 5mLof Ferrous tartrate solution,and dilute with Buffer solutionto volume.Determine the absorbances of both solutions at the wavelength of maximum absorbance at about 520nm,with a suitable spectrophotometer,using the blank in the reference cell.Calculate the quantity,in mg,of C10H13NO4in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Methyldopa RSin the Standard solution;and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.