Medium: 0.01 N hydrochloric acid; 500 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C18H29NO3·HCl dissolved by employing UV absorption at the wavelength of maximum absorbance at about 274 nm on filtered portions of the solution under test in comparison with a Standard solution having a known concentration of USP Betaxolol Hydrochloride RS in the same Medium. A 5-cm pathlength cell may be used for lower dosage levels.

Tolerances— Not less than 80% (Q) of the labeled amount of C18H29NO3·HCl is dissolved in 30 minutes.

Procedure for content uniformity— Place 1 Tablet in a volumetric flask of appropriate size to obtain a concentration, based on the labeled amount of betaxolol hydrochloride per Tablet, of about 0.1 mg per mL when diluted. Add an amount of 0.1 N hydrochloric acid equal to about 70% of the volume of the flask, shake by mechanical means until dissolved, dilute with 0.1 N hydrochloric acid to volume, and mix. Filter the mixture, discarding the first 20 mL of the filtrate. Concomitantly determine the absorbances of the clear filtrate and of a Standard solution of USP Betaxolol Hydrochloride RS in 0.1 N hydrochloric acid having a known concentration of about 0.1 mg per mL, in 1-cm cells, at the wavelength of maximum absorbance at about 274 nm, using 0.1 N hydrochloric acid as the blank. Calculate the quantity, in mg, of betaxolol hydrochloride (C18H29NO3·HCl) in the Tablet taken by the formula: in which C, is the concentration, in mg per mL, of USP Betaxolol Hydrochloride RS in the Standard solution; V is the volume, in mL, of 0.1 N hydrochloric acid used to dissolve the Tablet; and AU and AS are the absorbances of the solution from the Tablet and the Standard solution, respectively.

(Official January 1, 2007)

Mobile phase— Prepare a filtered mixture of 0.025 M pH 6.0 ammonium phosphate buffer, acetonitrile, and methanol (35:35:30). Mix, and degas under vacuum while stirring. Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluent— Prepare a mixture of acetonitrile and water (1:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Betaxolol Hydrochloride RS in Diluent to obtain a solution having a known concentration of about 2 mg per mL.

Assay preparation— Dissolve not fewer than 20 Tablets in an appropriate accurately measured volume of Diluent so that the final concentration, based on the labeled amount per Tablet, is about 2 mg of betaxolol hydrochloride per mL. Sonicate until the Tablets are disintegrated. Cool to room temperature, dilute with Diluent to volume, mix, and filter. Use the clear filtrate as the Assay preparation.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 273-nm detector and a 4.6-mm × 15-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, record the chromatogram, and measure the peak response as directed for Procedure: the tailing factor is not more than 3.0, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of betaxolol hydrochloride (C18H29NO3·HCl) in each Tablet taken by the formula: in which C is the concentration, in mg per mL, of USP Betaxolol Hydrochloride RS in the Standard preparation; V is the volume of Diluent used to dissolve the Tablets; N is the number of Tablets taken; and rU and rS are the betaxolol peak responses obtained from the Assay preparation and the Standard preparation, respectively.