A:Infrared Absorption á197Kñ.

B: 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 filtered and degassed mixture of solvent hexane,isopropyl alcohol,alcohol,and trifluoroacetic acid (80:14:6:0.5).Increase or decrease the percent of hexane or alcohol,but keep the percent of isopropyl alcohol constant.Make other adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Transfer about 10mg of USP Racemic Tiagabine Hydrochloride Mixture RS,accurately weighed,to a 100-mLvolumetric flask.Add a few drops of methanol to dissolve,dilute with isopropyl alcohol to volume,and mix.

Test solution— Transfer about 50mg of Tiagabine Hydrochloride,accurately weighed,to a 25-mLvolumetric flask;add a few drops of methanol to dissolve;dilute with isopropyl alcohol to volume;and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 260-nm detector and a 4.6-mm ×25-cm column that contains packing L40.The flow rate is about 0.8mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.76for the(S)-(+)isomer and 1.0for the (R)-(-)isomer;and the resolution,R,between the (S)-(+)and (R)-(-)isomers is not less than 2.0.

Procedure— Inject about 10µLof the Test solutioninto the chromatograph,record the chromatogram,and measure the responses of the major peaks obtained from the (S)-(+)and (R)-(-)isomers.Calculate the percentage of the(S)-(+)isomer in the portion of Tiagabine Hydrochloride taken by the formula: in which rSand rRare the peak responses of the(S)-(+)and(R)-(-)isomers,respectively:not more than 0.5%of the(S)-(+)isomer is found.

Solution A— Use a filtered and degassed solution of water adjusted with phosphoric acid to a pHof 2.3.

Solution B— Use filtered and degassed acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard stock solution— Dissolve an accurately weighed quantity of USP Tiagabine Hydrochloride RSin water to obtain a solution having a known concentration of about 1mg per mL.

Standard solution— Dilute a portion of the Standard stock solutionquantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.001mg per mL.

Resolution solution— Dissolve an accurately weighed quantity of USP Tiagabine Related Compound A RSin water to obtain a solution having a known concentration of about 1mg per mL.Transfer 1.0mLof this solution and 1.0mLof the Standard stock solutionto a 10-mLvolumetric flask,dilute with water to volume,and mix.

Test solution— Transfer about 100mg of Tiagabine Hydrochloride,accurately weighed,to a 100-mLvolumetric flask.Dissolve in and dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L1.The flow rate is about 1.0mLper minute.The chromatograph is programmed as follows. Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between tiagabine hydrochloride and tiagabine related compound Ais not less than 9.0;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%.

Interference check— Inject water as the blank:no interfering peaks are observed.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure all the peak responses.Calculate the percentage of each impurity in the portion of Tiagabine Hydrochloride taken by the formula: in which Fis the relative response factor (see the accompanying table for values)for each impurity;riis the peak response for each impurity obtained from the Test solution;and rsis the sum of the responses of all the peaks,excluding the solvent peaks.(See the accompanying table for limits of individual impurities.)Not more than 1.0%of total impurities is found.

Diluent— Prepare a mixture of methanol and water (1:1).

Buffer solution— Dissolve 1.38g of monobasic sodium phosphate in 1000mLof water,and adjust with phosphoric acid to a pHof 2.0.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solutionand acetonitrile (65:35).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard preparation— Prepare a solution of butylparaben in Diluenthaving a concentration of about 0.4mg per mL.

Standard stock preparation— Dissolve an accurately weighed quantity of USP Tiagabine Hydrochloride RSin Diluentto obtain a solution having a known concentration of about 1mg per mL.

Standard preparation— Transfer 10.0mLof the Standard stock preparationand 10.0mLof the Internal standard preparationto a 100-mLvolumetric flask,dilute with Diluentto volume,and mix.

Assay preparation— Transfer about 100mg of Tiagabine Hydrochloride,accurately weighed,to a 100-mLvolumetric flask;dilute with Diluentto volume;and mix.Transfer 10.0mLof this solution and 10.0mLof the Internal standard preparationto a 100-mLvolumetric flask,dilute with Diluentto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L1.The flow rate is about 1.0mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between tiagabine hydrochloride and butylparaben is not less than 5.5;and the relative standard deviation of the peak response ratios for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak areas.Calculate the quantity,in mg,of C20H25NO2S2·HCl in the portion of Tiagabine Hydrochloride taken by the formula: in which Cis the concentration,in mg per mL,of USP Tiagabine Hydrochloride RSin the Standard preparation;and RUand RSare the peak area ratios of tiagabine hydrochloride to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.