Medium: pH6.8phosphate buffer (see under Buffer Solutionsin the section Reagents,Indicators,and Solutions);900mL.

Apparatus 2: 50rpm.

Time: 20minutes.

Standard solution— Dissolve an accurately weighed quantity of USP Guanadrel Sulfate RSin Mediumto obtain a solution having a known concentration of about 0.5mg per mL.Transfer 5.0mLof this solution to a 200-mLvolumetric flask,dilute with Mediumto volume,and mix.

Working color reagent preparation— Transfer 50.0mLof the Color reagent preparation,prepared as directed for Procedure for content uniformityin Uniformity of dosage units,to a 500-mLvolumetric flask,dilute with water to volume,and mix.

Color reagent blank— [NOTE—Prepare this solution concurrently with the preparation of the Standard solution and the solution under test.]Transfer 40.0mLof Mediumto a container,add 8.0mLof Working color reagent preparation,and mix.

Procedure— After 20minutes,withdraw a portion of the solution under test,and filter immediately.For Tablets containing less than 25mg per Tablet,transfer 20.0mLof the filtered solution to a container.For Tablets containing 25mg or more,transfer 10.0mLof the filtered solution and 10.0mLof Mediumto a container.Transfer 20.0mLof the Standard solutionto another,similar container.Separately add 4.0mLof Working color reagent preparationto the solution of the test specimen and the Standard solution,and mix.Using a suitable spectrophotometer,determine the absorbances of the solutions obtained from the test specimen and the Standard solution,in 5-cm cells,at the wavelength of maximum absorbance at about 494nm,using the Color reagent blankin the reference cell.[NOTE—Once the Working color reagent preparation has been added to the filtered dissolution specimens and mixed,determine the absorbances so that none of the solutions stands for less than 20minutes or more than 80minutes.]Calculate the amount of (C10H19N3O2)2·H2SO4dissolved by comparison of the absorbances obtained with the solutions obtained from the Standard solutionand the solution under test.

Tolerances— Not less than 70%(Q)of the labeled amount of (C10H19N3O2)2·H2SO4is dissolved in 20minutes.

Procedure for content uniformity—

Color reagent preparation— Prepare separately sodium nitroferricyanide solution (1in 10),potassium ferricyanide solution (1in 10),and sodium hydroxide solution (1in 10),and store in separate amber-colored bottles.Mix an equal and sufficient volume of each of these solutions,in the order listed,and allow to stand for about 15minutes.The solution changes from a deep red-black to a yellow-green color.Prepare a 1in 10dilution of the solution in water to obtain the Color reagent preparation.[NOTE—Prepare this Color reagent preparation on the day of use.The 10%aqueous solutions are stable for about 2months.]

Standard preparation— Dissolve an accurately weighed quantity of USP Guanadrel Sulfate RSin water to obtain a solution having a known concentration of about 0.1mg per mL.Transfer 10.0mLof this solution to a container,and proceed as directed under Procedure.

Test preparation— Transfer 1Tablet to a 100-mLvolumetric flask,dilute with water to volume,and shake the flask vigorously for about 4minutes.Transfer not less than 25mLof the solution to a vial,and centrifuge for 10minutes.Transfer an accurately measured volume of this solution,equivalent to 1mg of guanadrel sulfate,to another container,and dilute,if necessary,with an accurately measured volume of water to a volume of 10.0mL.Mix,and proceed as directed under Procedure.

Procedure— Separately add 4.0mLof the Color reagent preparationto the Standard preparation,the Test preparation,and 10.0mLof water to provide the blank.Mix the solutions,and allow to stand for 10minutes.Within 5minutes,determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 494nm,with a suitable spectrophotometer,against the reagent blank.Calculate the quantity,in mg,of (C10H19N3O2)2·H2SO4in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of guanadrel sulfate in the Tablet;Cis the concentration,in mg per mL,of USP Guanadrel Sulfate RSin the Standard preparation;Dis the concentration,in mg per mL,of guanadrel sulfate in the Test preparation,based upon the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solutions from the solution under test and the Standard preparation,respectively.

Mobile phase,Standard preparation,Resolution solution,and Chromatographic system— Proceed as directed in the Assayunder Guanadrel Sulfate.

Assay preparation— Transfer a number of Tablets,equivalent to about 100mg of guanadrel sulfate,to a container.Add an accurately measured volume of Mobile phaseto obtain a final concentration of about 10mg of guanadrel sulfate per mLof Mobile phase,shake by mechanical means for 20minutes,and centrifuge if necessary.

Procedure— Proceed as directed for Procedurein the Assayunder Guanadrel Sulfate.Calculate the quantity,in mg,of guanadrel sulfate [(C10H19N3O2)2·H2SO4]in the Tablets taken by the formula: in which Vis the volume,in mL,of Mobile phaseadded to the Tablets,and the other terms are as defined in the Assayunder Guanadrel Sulfate.