Medium: pH 6.8 phosphate buffer (see under Buffer Solutions in the section Reagents, Indicators, and Solutions); 900 mL.

Apparatus 2: 50 rpm.

Time: 20 minutes.

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

Working color reagent preparation— Transfer 50.0 mL of the Color reagent preparation, prepared as directed for Procedure for content uniformity in Uniformity of dosage units, to a 500-mL volumetric 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 40.0 mL of Medium to a container, add 8.0 mL of Working color reagent preparation, and mix.

Procedure— After 20 minutes, withdraw a portion of the solution under test, and filter immediately. For Tablets containing less than 25 mg per Tablet, transfer 20.0 mL of the filtered solution to a container. For Tablets containing 25 mg or more, transfer 10.0 mL of the filtered solution and 10.0 mL of Medium to a container. Transfer 20.0 mL of the Standard solution to another, similar container. Separately add 4.0 mL of Working color reagent preparation to 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 494 nm, using the Color reagent blank in 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 20 minutes or more than 80 minutes.] Calculate the amount of (C10H19N3O2)2·H2SO4 dissolved by comparison of the absorbances obtained with the solutions obtained from the Standard solution and the solution under test.

Tolerances— Not less than 70% (Q) of the labeled amount of (C10H19N3O2)2·H2SO4 is dissolved in 20 minutes.

Procedure for content uniformity—

Color reagent preparation— Prepare separately sodium nitroferricyanide solution (1 in 10), potassium ferricyanide solution (1 in 10), and sodium hydroxide solution (1 in 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 15 minutes. The solution changes from a deep red-black to a yellow-green color. Prepare a 1 in 10 dilution 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 2 months.]

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

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

Procedure— Separately add 4.0 mL of the Color reagent preparation to the Standard preparation, the Test preparation, and 10.0 mL of water to provide the blank. Mix the solutions, and allow to stand for 10 minutes. Within 5 minutes, determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 494 nm, with a suitable spectrophotometer, against the reagent blank. Calculate the quantity, in mg, of (C10H19N3O2)2·H2SO4 in the Tablet taken by the formula: in which T is the labeled quantity, in mg, of guanadrel sulfate in the Tablet; C is the concentration, in mg per mL, of USP Guanadrel Sulfate RS in the Standard preparation; D is 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 AU and AS are the absorbances of the solutions from the solution under test and the Standard preparation, respectively.

(Official January 1, 2007)

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

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

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