A: Infrared Absorption á197Mñ.

B: Asolution (10mg per mL)responds to the tests for Sulfate á191ñ.

Test solution: 10mg per mL,in methanol.

Organic phase— Prepare a mixture of methanol and acetonitrile (610:390).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Aqueous phase— Dissolve 11g of sodium 1-heptanesulfonate in 1000mLof water,add 5.0mLof triethylamine,adjust with phosphoric acid to a pHof 2.70±0.05,and filter through a filter having a porosity of 0.5µm or finer.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Solvent mixture— Prepare a mixture of Organic phaseand Aqueous phase(600:400).

Test solution— Transfer about 50mg of Penbutolol Sulfate to a 25-mLvolumetric flask,dissolve in and dilute with Solvent mixtureto volume,and mix.

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

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 271-nm detector,a preinjection guard column that contains packing L4,and a 4.6-mm ×25-cm analytical column that contains packing L1and is maintained at a constant temperature between ambient and 40,and is programmed to provide variable mixtures of Organic phaseand Aqueous phase.Before each injection,the system is equilibrated with a mobile phase consisting of a mixture of 60%Organic phaseand 40%Aqueous phase.After each injection,this composition of the mobile phase is maintained for 15minutes,then the proportion of Organic phaseis increased linearly over the next 20minutes so that the mobile phase consists of 80%Organic phaseand 20%Aqueous phase.The proportion of Organic phaseis then decreased to 60%over 1minute.The flow rate is about 1mLper minute.Chromatograph the Diluted test solution,and record the peak responses as directed for Procedure:the resolution,R,between the penbutolol peak and any impurity peak is not less than 1.5,and the tailing factor is not more than 2,when calculated by the formula: in which W0.1is the width of the peak at 10%of peak height.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 20µL)of the Solvent mixture,the Test solution,and the Diluted test solutioninto the chromatograph,and measure the peak responses for all the peaks.Calculate the percentage of each individual impurity in the Penbutolol Sulfate taken by the formula: in which riis the peak response for an individual impurity in the chromatogram of the Test solution,and rDis the penbutolol peak response obtained from the Diluted test solution:not more than 1.2%of any impurity is found.

Organic phase— Prepare a mixture of methanol and acetonitrile (610:390).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Aqueous phase— Dissolve 11g of sodium 1-heptanesulfonate in 1000mLof water,add 5.0mLof triethylamine,adjust with phosphoric acid to a pHof 2.70±0.05,and filter through a filter having a porosity of 0.5µm or finer.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Mobile phase— Prepare a mixture of Organic phaseand Aqueous phase(650:350).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of 3,4-dimethylbenzophenone in Mobile phasecontaining about 0.01mg per mL.

Standard preparation— Transfer about 24mg of USP Penbutolol Sulfate RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Internal standard solutionto volume,and mix.

Assay preparation— Transfer about 24mg of Penbutolol Sulfate,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Internal standard solutionto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 271-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.9for penbutolol and 1.0for 3,4-dimethylbenzophenone,and the resolution,R,between the penbutolol peak and the 3,4-dimethylbenzophenone peak is not less than 1.5,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas of the responses for the major peaks.Calculate the quantity,in mg,of (C18H29NO2)2·H2SO4in the portion of Penbutolol Sulfate 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 ratios of the penbutolol peak response to the internal standard peak response obtained from the Assay preparationand the Standard preparation,respectively.