Medium: water; 500 mL.

Apparatus 2: 100 rpm.

Time: 60 minutes.

Procedure— Determine the amount of isopropamide (C23H33N2O) dissolved from UV absorbances at the wavelength of maximum absorbance at about 258 nm of filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Isopropamide Iodide RS in the same medium.

Tolerances— Not less than 70% (Q) of the labeled amount of C23H33N2O is dissolved in 60 minutes.

Procedure for content uniformity— Crush and transfer 1 Tablet to a 100-mL volumetric flask with the aid of about 50 mL of water, and shake by mechanical means for 30 minutes. Dilute with water to volume, mix, and filter, discarding the first 20 mL of the filtrate. Concomitantly determine the absorbances of this solution and a Standard solution of USP Isopropamide Iodide RS in the same medium having a known concentration of about 70 µg per mL, in 5-cm cells at 280 nm and at the wavelength of maximum absorbance at about 258 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of isopropamide (C23H33N2O) in the Tablet taken by the formula: in which 353.53 and 480.43 are the molecular weights of isopropamide and isopropamide iodide, respectively; T is the labeled quantity, in mg, of isopropamide in the Tablet; C is the concentration, in µg per mL, of USP Isopropamide Iodide RS in the Standard solution; D is the concentration, in µg per mL, of isopropamide in the test solution, based upon the labeled quantity per Tablet and the extent of dilution; and AU and AS are the absorbances of the test solution and the Standard solution, respectively, at the wavelengths indicated by the subscripts.

(Official January 1, 2007)

Ion-exchange column— Insert a small pledget of glass wool in the bottom of a 6-mm × 240-mm glass tube fitted with a stopcock, fill the tube with water, and add an aqueous slurry of a suitable anion-exchange resin, chloride form (soaked in water for not less than 24 hours prior to use), until a height of about 200 mm is reached. Wash the column with 50 mL of water, and use without delay.

Standard preparation— Transfer about 135 mg of USP Isopropamide Iodide RS, accurately weighed, to a 250-mL volumetric flask, and dissolve in 150 mL of water. Add 5 mL of aluminum chloride solution (1 in 10) and 2 mL of ammonium hydroxide, then dilute with water to volume, mix, and filter, discarding the first 15 mL of the filtrate. Use the subsequent filtrate as directed for Procedure.

Assay preparation— Weigh and finely powder not less than 25 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of isopropamide, to a 250-mL volumetric flask, add 150 mL of water, and shake by mechanical means for 60 minutes. Add 5 mL of aluminum chloride solution (1 in 10) and 2 mL of ammonium hydroxide, dilute with water to volume, mix, and filter, discarding the first 15 mL of the filtrate. Use the subsequent filtrate as directed for Procedure.

Procedure— Pipet 50.0 mL each of the Standard preparation and the Assay preparation, respectively, onto separate ion-exchange columns, and collect the eluates in separate 200-mL volumetric flasks. Regulate the flow of effluent so that it does not exceed 40 drops per minute, and when the liquid level reaches the top of each column, add successively two 5-mL portions and one 10-mL portion of water to each column, allowing each portion just to enter the column before adding the next portion of water. After the eluates have been collected, dilute the contents of each flask with water to volume, and mix. Concomitantly determine the absorbances of the solutions in 5-cm cells at 280 nm and at the maximum at about 258 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of isopropamide (C23H33N2O) in the portion of Tablets taken by the formula: in which 353.53 and 480.43 are the molecular weights of isopropamide and isopropamide iodide, respectively; C is the concentration, in µg per mL, of USP Isopropamide Iodide RS in the Standard preparation; and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively, at the wavelengths indicated by the subscripts.