A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Solution: 20µg per mL.

Medium: hydrochloric acid in methanol (1in 1200).

C: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

Mobile phase— Prepare a mixture of 0.05Msodium acetate,previously adjusted with glacial acetic acid to a pHof 5.0,and acetonitrile (65:35),and filter through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Decreasing the acetonitrile concentration results in less resolution between pindolol and impurities that elute on the tail of the pindolol peak;increasing the acetonitrile concentration results in less resolution between impurities with longer retention times.

Resolution solution— Prepare as directed for Resolution solutionin the Assay.

Test solution— Use the stock solution used to prepare the Assay preparationin the Assay.

Chromatographic system (see Chromatography á621ñ)— Proceed as directed in the Chromatographic systemunder the Assay.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 10µL)of the Resolution solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for all of the peaks.Calculate the percentage of each impurity in the portion of Pindolol taken by the formula: in which Cis the concentration,in mg per mL,of USP Pindolol RSin the Resolution solution,Wis the weight,in mg,of the portion of Pindolol taken to prepare the Test solution,rUis the peak response of an individual impurity,and rSis the pindolol peak response obtained from the Resolution solution.Not more than 0.5%of any individual impurity is found,and the total of all impurities does not exceed 2.0%.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Prepare a mixture of 0.05Msodium acetate,previously adjusted with glacial acetic acid to a pHof 5.0,and acetonitrile (65:35),and filter through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Resolution solution— Prepare a solution in Mobile phasehaving known concentrations of about 0.005mg of USP Pindolol RSper mLand about 0.005mg of indole per mL.

Standard preparation— Transfer about 100mg of USP Pindolol RS,accurately weighed,to a 100-mLvolumetric flask,add about 90mLof Mobile phase,and dissolve by sonicating for about 5minutes.Cool,dilute with Mobile phaseto volume,and mix.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Assay preparation— Transfer about 100mg of Pindolol,accurately weighed,to a 100-mLvolumetric flask,add about 90mLof Mobile phase,and dissolve by sonicating for about 5minutes.Cool,dilute with Mobile phaseto volume,and mix.Transfer 5.0mLof this stock solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 219-nm detector and a 4.6-mm ×15-cm column containing 3-µm packing L10.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the responses as directed for Procedure:the relative retention times are about 0.5for indole and 1.0for pindolol,the resolution,R,between the indole and pindolol is not less than 7,the column efficiency determined from the pindolol peak is not less than 3000theoretical plates,and the relative standard deviation of the pindolol peak response for replicate injections is not more than 2%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 10µL)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 C14H20N2O2in the portion of Pindolol taken by the formula: in which Cis the concentration,in mg per mL,of USP Pindolol RSin the Standard preparation,and rUand rSare the pindolol peak responses obtained from the Assay preparationand the Standard preparation,respectively.