Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C19H24N2O3·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 302 nm of filtered portions of the solution under test, suitably diluted with water, if necessary, in comparison with a Standard solution having a known concentration of USP Labetalol Hydrochloride RS in the same Medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C19H24N2O3·HCl is dissolved in 45 minutes.

(Official January 1, 2007)

Mobile phase , Standard preparation, and Chromatographic system—Proceed as directed in the Assay under Labetalol Hydrochloride.

Assay preparation— Transfer an accurately counted number of Tablets, equivalent to about 2000 mg of labetalol hydrochloride, to a 500-mL volumetric flask, add 200 mL of water, and shake by mechanical means for 60 minutes. Dilute with water to volume, and mix. Filter the solution through a filter of 0.5 µm or finer porosity, discarding the first few mL of the filtrate. Transfer 10.0 mL of the filtrate to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Procedure— Separately inject equal volumes (about 5 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the area responses for the major peaks. Calculate the quantity, in mg, of labetalol hydrochloride (C19H24N2O3·HCl) in each Tablet taken by the formula: in which C is the concentration, in mg per mL, of USP Labetalol Hydrochloride RS in the Standard preparation; N is the number of Tablets taken; and rU and rS are the peak area responses obtained from the Assay preparation and the Standard preparation, respectively.