Test specimen— Transfer one or more Tablets,equivalent to about 200mg of metoprolol succinate,to a stoppered centrifuge tube.Add about 40mLof pH6.8phosphate buffer (see Buffer Solutionsin the section Reagents,Indicators,and Solutions)and 40mLof methylene chloride,and shake for 5minutes.Centrifuge,filter,and use the aqueous phase as the Test solution.Transfer 3mLof the Test solutionto a separator,add 2mLof ammonium hydroxide,and extract with 20mLof methylene chloride.Filter the methylene chloride phase.Grind 1mLof the filtrate with 300mg of potassium bromide,dry in a current of warm air,and prepare a disk:the IRspectrum of the Test specimenexhibits maxima only at the same wavelengths as that obtained from a similar preparation of USP Metoprolol Succinate RS(presence of metoprolol).

Test specimen— Transfer 5mLof the Test solutionprepared as directed for Identificationtest Ato a glass-stoppered test tube,add 2mLof 5Nhydrochloric acid,and extract with 5mLof ether.Filter the ether phase.Grind 2mLof the filtrate with 300mg of potassium bromide,dry in a current of warm air,and prepare a disk:the IRspectrum of the Test specimenexhibits maxima only at the same wavelengths as that obtained from a similar preparation of succinic acid (presence of succinate).

Time (hours)	Amount dissolved
1	not more than 25%
4	between 20%and 40%
8	between 40%and 60%
20	not less than 80%

pH3.0Phosphate buffer— Mix 50mLof 1Mmonobasic sodium phosphate and 8.0mLof 1Mphosphoric acid,and dilute with water to 1000mL.If necessary,adjust with 1Mmonobasic potassium phosphate or 1Mphosphoric acid to a pHof 3.0.

Mobile phase— Prepare a filtered and degassed mixture of pH3.0Phosphate bufferand acetonitrile (375:125).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve a quantity of USP Metoprolol Succinate RS,accurately weighed,in Mobile phaseto obtain a solution having a known concentration of about 0.05mg per mL.

Test stock solution— Transfer 1Tablet,accurately weighed,to a volumetric flask of suitable capacity to obtain a solution having a concentration of about 1mg per mLof metoprolol succinate.Add about 5mLof water,and allow the Tablet to disintegrate.Add a volume of alcohol such that when diluted to volume,the concentration of alcohol is 30%.Shake for 30minutes.Add a portion of 0.1Nhydrochloric acid equivalent to about one half of the flask volume,and shake for 30minutes.Dilute with 0.1Nhydrochloric acid to volume,and mix.

Test solution— Filter the Test stock solution,and discard the first 10mLof the filtrate.Dilute the filtrate quantitatively with Mobile phaseto obtain a solution containing about 0.05mg per mLof metoprolol succinate.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 4-mm ×12.5-cm column that contains packing L7.The flow rate is about 1mLper 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 2.0%.

Procedure— Separately inject equal volumes (about 40µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of metoprolol succinate (C15H25NO3)2·C4H6O4in the Tablet taken by the formula: in which Cis the concentration,in mg per mL,of USP Metoprolol Succinate RSin the Standard solution;Vis the volume of the Test stock solutionused to prepare the Test solution;and rUand rSare the peak responses obtained from the Test solutionand the Standard solution,respectively.