Chromatographic purity—
Buffer—
Prepare a solution of 0.025 M monobasic potassium phosphate containing 0.1% (w/v) of tetrabutylammonium bromide. Adjust with 0.025 M phosphoric acid to a pH of 3.0.
Mobile phase—
Prepare a suitable filtered and degassed mixture of
Buffer and acetonitrile (85:15). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Resolution solution—
Prepare a solution in
Mobile phase containing 2.0 mg of
USP Betaxolol Hydrochloride RS and 1 mg of alprenolol hydrochloride per mL.
Test preparation—
Prepare a solution of Betaxolol Hydrochloride in Mobile phase containing 2.0 mg per mL.
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 5-µm packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Resolution solution, and record the peak responses as directed for
Procedure: the relative retention times are about 0.9 for alprenolol and 1.0 for betaxolol; the resolution,
R, between the two peaks is not less than 1.0; the tailing factors for the two peaks are not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Inject about 20 µL of the
Test preparation into the chromatograph, record the chromatogram, and measure the areas for the peaks.
[NOTE—Allow the elution to continue for about five times the elution time of the betaxolol peak before making the next injection.
] Calculate the percentage of each impurity by the same formula:
100(ri / rS),
in which
ri is the response of each individual peak, other than the main betaxolol peak, in the chromatogram obtained from the
Test preparation, and
rS is the sum of the responses of all the peaks obtained in the chromatogram from the
Test preparation: the sum of all impurities found is not more than 1.0%.
Assay—
Dissolve about 300 mg of Betaxolol Hydrochloride, accurately weighed, in 50 mL of glacial acetic acid. Add 7 mL of
mercuric acetate TS, and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 34.39 mg of C
18H
29NO
3·HCl.
;)
for 2 hours: it loses not more than 1.0% of its weight.