A: Examine the chromatograms obtained in the test for Chromatographic purity:the principal spot obtained from the Test solutionis similar in RFvalue,color,and intensity to that obtained from the Standard stock solution.

B: The retention time exhibited by pindolol in the chromatogram of the Assay preparationcorresponds to that of pindolol in the chromatogram of the Standard preparation,as obtained in the Assay.

Medium: 0.1Nhydrochloric acid;500mL.

Apparatus 2: 50rpm.

Time: 15minutes.

Mobile phase and Chromatographic system—Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Pindolol RSin Dissolution Mediumto obtain a solution having a known concentration of about 0.002Jmg per mL,Jbeing the labeled quantity,in mg,of pindolol in each Tablet.Mix equal volumes of this solution and of Mobile phaseto obtain the Standard solution.

Resolution solution— Dissolve a quantity of nortriptyline hydrochloride in Standard solutionto obtain a solution having a concentration of about 0.005mg of nortriptyline hydrochloride per mL.

Test solution— Filter a portion of the solution under test.Mix equal volumes of the filtrate and of Mobile phaseto obtain the Test solution.

Procedure— Proceed as directed for Procedureunder the Assay.Calculate the quantity of C14H20N2O2dissolved by the formula: in which Cis the concentration,in mg per mL,of USP Pindolol RSin the Standard solution;and rUand rSare the pindolol peak responses obtained from the Test solutionand the Standard solution,respectively.

Tolerances— Not less than 80%(Q)of the labeled amount of C14H20N2O2is dissolved in 15minutes.

p-Dimethylaminobenzaldehyde spray— Dissolve 1g of p-dimethylaminobenzaldehyde in a mixture of 50mLof hydrochloric acid and 50mLof alcohol,and mix.[NOTE—Store this solution in a tightly closed,light-resistant container,and discard after 4weeks.]

Solvent mixture— Prepare a solution of methanol and glacial acetic acid (99:1).

Standard stock solution— Dissolve an accurately weighed quantity of USP Pindolol RSin Solvent mixtureto obtain a solution containing 5.0mg per mL.

Standard solution 1— Dilute an accurately measured volume of Standard stock solutionquantitatively and stepwise with Solvent mixtureto obtain a solution containing 0.025mg per mL.

Standard solution 2— Dilute 6.0mLof Standard solution 1with Solvent mixtureto 10.0mL,and mix.

Standard solution 3— Dilute 4.0mLof Standard solution 1with Solvent mixtureto 10.0mL,and mix.

Standard solution 4— Dilute 2.0mLof Standard solution 1with Solvent mixtureto 10.0mL,and mix.

Test solution— [NOTE—Prepare this solution immediately before use,and apply last.]Transfer a portion of powdered Tablets,equivalent to 50mg of pindolol,to a 50-mLflask,add 10.0mLof Solvent mixture,insert the stopper in the flask,and shake by mechanical means for 15minutes.Centrifuge a portion of the resultant suspension,and promptly test the clear supernatant.

Procedure— Prepare a lined chromatographic chamber (see Chromatography á621ñ)with a developing solvent consisting of a mixture of methylene chloride,methanol,and formic acid (75:23.5:1.5),and equilibrate for 30minutes.Separately apply 2-µLportions of the Standard stock solution,each of the Standard solutions,and the Test solutionto a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel.Place the plate in the chromatographic chamber,and allow the solvent front to move about two-thirds of the length of the plate.Remove the plate from the chamber,immediately spray with the p-Dimethylaminobenzaldehyde spray,heat the plate at 60for 15minutes,and promptly examine the chromatogram:no individual secondary spot observed in the chromatogram of the Test solutionis greater in size or intensity than the principal spot observed in the chromatogram of Standard solution 1,corresponding to 0.5%,and the total of any such spots observed does not exceed 3.0%.[NOTE—In a valid determination,spots from all solutions must be visible.]

Ammonium carbonate solution— Dissolve 300mg of ammonium carbonate in 50mLof water,and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,methanol,and Ammonium carbonate solution(475:475:50),making adjustments,if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Prepare a solution of USP Pindolol RSin Mobile phaseto obtain a solution having a known concentration of about 0.2mg per mL.

Resolution solution— Dissolve a quantity of nortriptyline hydrochloride in Standard preparationto obtain a solution having a concentration of about 0.2mg of nortriptyline hydrochloride 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 pindolol,to a 100-mLvolumetric flask.Add 4mLof water,and sonicate for 2minutes,with occasional shaking to disperse the powder.Add 30mLof Mobile phase,sonicate for 15minutes,and allow to cool.Dilute with Mobile phaseto volume,mix,and filter.Use the clear filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L16.The flow rate is about 3mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution between pindolol and nortriptyline is not less than 1.5.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— 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.The relative retention times are about 0.6for pindolol and 1.0for nortriptyline.Calculate the quantity,in mg,of pindolol (C14H20N2O2)in the portion of Tablets 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.