A: Infrared Absorption 197M—

B: Infrared Absorption 197M—

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Filter a portion of the solution under test, transfer 10.0 mL of the filtrate to a suitable capped bottle, and add 5.0 mL of water, 1.0 mL of 5 N sodium hydroxide, and 25.0 mL of n-heptane. Cap the bottle, shake by mechanical means for 5 minutes, and allow the layers to separate, centrifuging if necessary, to obtain clear upper (n-heptane) and lower (aqueous) extracts. Determine the quantity, in µg, of propranolol hydrochloride (C16H21NO2·HCl) in each mL of the n-heptane extract by employing UV absorption at the wavelength of maximum absorbance at about 293 nm, in comparison with an n-heptane Standard solution obtained by similarly treating and extracting a mixture of 5.0 mL of an aqueous solution having a known concentration of USP Propranolol Hydrochloride RS and 5.0 mL of a 0.005 N sodium hydroxide solution having a known concentration of USP Hydrochlorothiazide RS, using a blank consisting of the n-heptane extract obtained by similarly treating and extracting 10.0 mL of water. Determine the quantity, in µg, of hydrochlorothiazide (C7H8ClN3O4S2) in each mL of the aqueous extract by employing UV absorption at the wavelength of maximum absorbance at about 273 nm, in comparison with the aqueous extract remaining from the preparation of the n-heptane Standard solution, using as a blank the aqueous extract remaining from the preparation of the n-heptane blank extract. Calculate the quantity, in mg, of C16H21NO2·HCl dissolved by multiplying the quantity, in µg, of propranolol hydrochloride in each mL of the n-heptane extract from the solution under test by 2.25. Calculate the quantity, in mg, of C7H8ClN3O4S2 dissolved by multiplying the quantity, in µg, of hydrochlorothiazide in each mL of the aqueous extract from the solution under test by 1.44.

Tolerances— Not less than 80% (Q) of the labeled amount of C16H21NO2·HCl and not less than 80% (Q) of the labeled amount of C7H8ClN3O4S2 is dissolved in 30 minutes.

Procedure for content uniformity— Transfer a Tablet to a suitable container, and add 500.0 mL of 0.1 N hydrochloric acid. Shake until the Tablet has disintegrated, sonicate for 30 seconds, shake by mechanical means for 30 minutes, and then repeat the sonication and shaking. Centrifuge a portion of the solution, and transfer 6.0 mL of the clear supernatant and 15.0 mL of water to a suitable capped bottle. Add 1.0 mL of 5 N sodium hydroxide and 25.0 mL of n-heptane, cap the bottle, shake by mechanical means for 5 minutes, and allow the layers to separate, centrifuging, if necessary, to obtain clear upper (n-heptane) and lower (aqueous) layers (test solutions). Prepare a similar Standard solution by mixing 6.0 mL of 0.1 N hydrochloric acid, 3.0 mL of water, 6.0 mL of an aqueous solution having a known concentration of USP Propranolol Hydrochloride RS, and 6.0 mL of a 0.04 N sodium hydroxide solution having a known concentration of USP Hydrochlorothiazide RS, and proceeding as directed for the test solutions, beginning with “Add 1.0 mL of 5 N sodium hydroxide.” Prepare similar blank n-heptane and aqueous extracts by adding 6.0 mL of 0.1 N hydrochloric acid to 15.0 mL of water, and proceeding as directed for the test solutions, beginning with “Add 1.0 mL of 5 N sodium hydroxide”. Concomitantly determine the absorbances of the n-heptane test solution and the n-heptane Standard solution at the wavelength of maximum absorbance at about 293 nm, using the n-heptane blank extract to set the instrument. Calculate the quantity, in mg, of propranolol hydrochloride (C16H21NO2·HCl) in the Tablet taken by the formula: in which C is the concentration, in µg per mL, of USP Propranolol Hydrochloride RS in the n-heptane Standard solution; and AU and AS are the absorbances at 293 nm of the n-heptane test solution and the n-heptane Standard solution, respectively. Concomitantly determine the absorbances of the aqueous test solution and the aqueous Standard solution at the wavelength of maximum absorbance at about 273 nm, using the aqueous blank extract to set the instrument. Calculate the quantity, in mg, of hydrochlorothiazide (C7H8ClN3O4S2) in the Tablet taken by the formula: in which C is the concentration, in µg per mL, of USP Hydrochlorothiazide RS in the aqueous Standard solution; and AU and AS are the absorbances at 273 nm of the aqueous test solution and the aqueous Standard solution, respectively.

Tetrabutylammonium hydroxide solution, Buffer, Mobile phase, and Chromatographic system— Proceed as directed under Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Benzothiadiazine Related Compound A RS in methanol to obtain a solution having a known concentration of about 0.5 mg per mL. Transfer an accurately measured volume of this solution, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.5 µg per mL.

Test solution— Use the Assay preparation prepared as directed in the Assay.

Chromatographic system— Proceed as directed under Assay, except to chromatograph the Standard solution: the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and Test solution into the chromatograph, record the chromatograms, and measure the peak areas. Calculate the percentage of benzothiadiazine related compound A in the portion of Tablets taken by the formula: in which C is the concentration in µg per mL, of USP Benzothiadiazine Related Compound A RS in the Standard solution; L is the amount, in mg, of hydrochlorothiazide in the portion of Tablets taken, based on the labeled amount; and rU and rS are the peak areas of benzothiadiazine related compound A obtained from the Test solution and Standard solution, respectively: not more than 1.0% is found.

(Official January 1, 2007)

Tetrabutylammonium hydroxide solution— Use a suitable aqueous or methanolic solution having a known concentration of tetrabutylammonium hydroxide.

Buffer— Dissolve 6.8 g of monobasic potassium phosphate in 1000 mL of water in a 2000-mL volumetric flask. Add 3.4 mL of phosphoric acid and a volume of Tetrabutylammonium hydroxide solution equivalent to about 2.6 g of tetrabutylammonium hydroxide, dilute with water to volume, and mix. Adjust, if necessary, with phosphoric acid or 10 N potassium hydroxide to a pH of 2.5 ± 0.1, and pass through a filter having a 0.5-µm or finer porosity.

Mobile phase— Prepare a suitable mixture of Buffer and methanol (850:150). Make adjustments if necessary (see System Suitability under Chromatography 621) so that the retention time of propranolol is between 12 and 25 minutes.

Standard hydrochlorothiazide stock solution— Transfer about 25 mg of USP Hydrochlorothiazide RS, accurately weighed, to a 100-mL volumetric flask, add 15 mL of methanol, and mix to dissolve. Dilute with Buffer to volume, and mix.

Standard propranolol hydrochloride stock solution— Dissolve an accurately weighed quantity of USP Propranolol Hydrochloride RS in Mobile phase to obtain a solution having a known concentration of about 0.25J mg per mL, J being the ratio of the labeled quantity, in mg, of propranolol hydrochloride to the labeled quantity, in mg, of hydrochlorothiazide per Tablet.

Standard preparation— Transfer 5.0 mL of Standard hydrochlorothiazide stock solution and 5.0 mL of Standard propranolol hydrochloride stock solution to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix. This solution contains about 50 µg of hydrochlorothiazide and 50J µg of propranolol hydrochloride per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 25 mg of hydrochlorothiazide, to a 500-mL volumetric flask. Add 5 mL of water, mix, and allow to stand for 5 minutes, with occasional swirling. Add 75 mL of methanol, mix, and sonicate for 10 minutes, with occasional swirling, adding ice to the bath, if necessary, to maintain the temperature at not more than 20. Add about 350 mL of Buffer to the flask, and sonicate for 10 minutes, with occasional swirling, maintaining the temperature of the bath at not more than 20. Dilute with Buffer to volume, and mix. Centrifuge a portion of this solution, if necessary, to obtain a clear solution (Assay preparation).

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 270-nm detector and a 4-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency determined from the propranolol peak is not less than 2500 theoretical plates; the tailing factor for the propranolol and hydrochlorothiazide peaks is not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%. [NOTE—The relative retention times are about 0.25 for benzothiadiazine related compound A, 0.4 for hydrochlorothiazide, and 1.0 for propranolol.]

Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantities, in mg, of propranolol hydrochloride (C16H21NO2·HCl) and hydrochlorothiazide (C7H8ClN3O4S2) in the portion of Tablets taken by the same formula: in which C is the concentration, in µg per mL, of the appropriate Reference Standard in the Standard preparation; and rU and rS are the peak responses of the corresponding analyte obtained from the Assay preparation and the Standard preparation, respectively.