Medium: water;900mL.

Apparatus 1(for hard gelatin capsules): 100rpm.

Apparatus 2(for soft gelatin capsules): 75rpm.

Time: 60minutes.

Mobile phaseand Chromatographic system— Proceed as directed in the test forContent of alpha lipoic acid.

Standard solution— Dissolve an accurately weighed quantity of USP Alpha Lipoic Acid RSin a mixture of acetonitrile and water (1:1)to obtain a solution having a known concentration of 1mg per mL.Transfer 1mLof this solution to a 50-mLvolumetric flask,dilute with water to volume,and mix to obtain a solution having a known concentration of about 0.02mg per mL.

Test solution— Withdraw a portion of the solution under test,and filter,discarding the first portion of the filtrate.Transfer an accurately measured aliquot to a volumetric flask,and dilute with water to volume to obtain a solution having an expected concentration of about 0.02mg of alpha lipoic acid per mL.

Procedure— Separately inject equal volumes (about 50µL)of theStandard solution and theTest solution into the chromatograph,record the chromatograms,and measure the peak areas.Determine the amount of C8H14O2S2dissolved by the formula: in whichCis the concentration of USP Alpha Lipoic Acid RSin theStandard solution;Dis the dilution factor of theTest solution;and rUand rSare the peak areas of alpha lipoic acid obtained from theTest solution and theStandard solution,respectively.

Tolerances— Not less than 70%of the labeled amount of C8H14O2S2is dissolved in 60minutes.

Mobile phase— Prepare a filtered and degassed mixture of 0.025Mphosphoric acid and acetonitrile (62:38).

Standard solution— Dissolve an accurately weighed quantity of USP Alpha Lipoic Acid RSin acetonitrile,and dilute quantitatively,and stepwise if necessary,with acetonitrile to obtain a solution having a known concentration of 0.05mg per mL.

Test solution 1(for hard gelatin capsules)— Empty and mix thoroughly the contents of not fewer than 20Capsules.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of alpha lipoic acid,to a suitable container,add about 70mLof a mixture of acetonitrile and water (1:1),and shake for 45minutes by mechanical means.Transfer to a 100-mLvolumetric flask,dilute with the mixture of acetonitrile and water (1:1)to volume,mix,and filter a portion of this preparation,discarding the first 5mLof the filtrate.Transfer 5.0mLof the remaining filtrate to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Test solution 2(for soft gelatin capsules)— Using a suitable cutting instrument,open an accurately counted number of Capsules equivalent to about 500mg of alpha lipoic acid.Transfer the contents and the shells to a suitable container with stopper,add 500.0mLof a mixture of acetonitrile and water (1:1),and shake for 45minutes by mechanical means.Filter a portion of this preparation,discarding the first 5mLof the filtrate.Transfer 5.0mLof the remaining filtrate to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 220-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph theStandard preparation,and record the peak responses as directed forProcedure:the tailing factor for alpha lipoic acid is not more than 1.2;the efficiency of the column is not less than 1300theoretical plates;and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20µL)of theStandard solution and the appropriateTest solution into the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of alpha lipoic acid in the portion of hard gel capsules taken by the formula: in whichCis the concentration,in mg per mL,of USP Alpha Lipoic Acid RSin theStandard solution;andrUandrSare the peak responses of alpha lipoic acid obtained fromTest solution 1and theStandard solution,respectively.Calculate the quantity,in mg,of alpha lipoic acid in each soft gel capsule taken by the formula: in whichCis the concentration,in mg per mL,of USP Alpha Lipoic Acid RSin theStandard solution;Nis the number of capsules taken;and rUand rSare the peak responses of alpha lipoic acid obtained fromTest solution 2and theStandard solution,respectively.