Solution: Sonicate a weighed portion of ground Tablets in sufficient methanol to obtain a solution containing about 0.4mg of penbutolol sulfate per mL.Filter this solution,and dilute a portion of the filtrate with methanol to obtain a solution containing about 0.06mg of penbutolol sulfate per mL.

Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Mobile phase— Dissolve 2g of ammonium acetate in 250mLof water,add 750mLof acetonitrile,mix,and adjust with glacial acetic acid to a pHof 6.0.Filter and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve an accurately weighed quantity of USP Penbutolol Sulfate RSquantitatively in water to obtain a stock solution having a known concentration of about 0.018mg per mL.Mix 10.0mLof this solution and 10.0mLof acetonitrile,and filter through a filter having a 0.5-µm or finer porosity.

Test solution— Filter about 30mLof the solution under test.Mix 10.0mLof the filtrate and 10.0mLof acetonitrile,and filter through a filter having a 0.5-µm or finer porosity.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 272-nm detector,a 4.6-mm ×15-cm column that contains 5-µm diameter packing L10.The flow rate is about 2.5mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Separately inject equal volumes (about 50µL)of the Standard solutionand the Test solutioninto the chromatograph,and measure the areas of the responses for the penbutolol peaks.Calculate the quantity,in mg,of (C18H29NO2)2·H2SO4dissolved by the formula: in which Cis the concentration,in mg per mL,of USP Penbutolol Sulfate RSin the Standard solution,and rUand rSare the penbutolol peak responses obtained from the Test solutionand the Standard solution,respectively.

Tolerances— Not less than 75%(Q)of the labeled amount of (C18H29NO2)2·H2SO4is dissolved in 30minutes.

100ri/rs,

Organic phase,Aqueous phase,Solvent mixture,and Chromatographic system— Proceed as directed in the test for Chromatographic purityunder Penbutolol Sulfate.

Test solution— Transfer an accurately weighed portion of powdered Tablets,equivalent to about 100mg of penbutolol sulfate,to a 50-mLvolumetric flask,dilute with Solvent mixtureto volume,mix,and filter.

Diluted test solution— Transfer 1.0mLof the Test solutionto a 100-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.

Procedure— Proceed as directed for Procedurein the test for Chromatographic purityunder Penbutolol Sulfate.Calculate the percentage of each individual impurity in the portion of Tablets taken by the formula: in which the terms are as defined therein:not more than 1.2%of any impurity is found.

Organic phase ,Aqueous phase,and Mobile phase—Proceed as directed in the Assayunder Penbutolol Sulfate.

Standard preparation— Dissolve an accurately weighed quantity of USP Penbutolol Sulfate RSquantitatively in Mobile phaseto obtain a solution having a known concentration of about 0.2mg per mL.

Resolution solution— Prepare a solution of 3,4-dimethylbenzophenone in Standard preparationcontaining about 0.01mg of 3,4-dimethylbenzophenone per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 20mg of penbutolol sulfate,to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Sonicate for about 10minutes,and filter a portion through a filter having a 0.5-µm or finer porosity,discarding the first 5mLof the filtrate.Use the clear filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 270-nm detector and a 4.6-mm ×15-cm column that contains 5-µm diameter packing L1.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for penbutolol and 1.0for 3,4-dimethylbenzophenone,and the tailing factor is not more than 1.4,when calculated by the formula: in which W0.1is the width of the peak at 10%of peak height,the resolution,R,between the penbutolol peak and the 3,4-dimethylbenzophenone peak is not less than 5,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of (C18H29NO2)2·H2SO4in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Penbutolol Sulfate RSin the Standard preparation,and rUand rSare the penbutolol peak responses obtained from the Assay preparationand the Standard preparation,respectively.