A: Infrared Absorption 197K.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds 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 percentage of hexane or alcohol, but keep the percentage of isopropyl alcohol constant. Make other adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— 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 0.8 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.76 for the (S)-(+) isomer and 1.0 for the (R)-() isomer; and the resolution, R, between the (S)-(+) and (R)-() isomers is not less than 2.0.

Procedure— Inject about 10 µL of the Test solution into the chromatograph, record the chromatogram, and measure the responses for 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 rS and rR are 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 pH of 2.3.

Solution B— Use filtered and degassed acetonitrile.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

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

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

Chromatographic system (see Chromatography 621)— 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 1.0 mL per 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 A is 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 20 µL) of the Standard solution and the Test solution into 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 F is the relative response factor (see the accompanying table for values) for each impurity; ri is the peak response for each impurity obtained from the Test solution; and rs is 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 1.38 g of monobasic sodium phosphate in 1000 mL of water, and adjust with phosphoric acid to a pH of 2.0.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solution and acetonitrile (65:35). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Standard preparation— Transfer 10.0 mL of the Standard stock preparation and 10.0 mL of the Internal standard preparation to a 100-mL volumetric flask, dilute with Diluent to volume, and mix.

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

Chromatographic system (see Chromatography 621)— 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 1.0 mL per 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 20 µL) of the Standard preparation and the Assay preparation into 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 C is the concentration, in mg per mL, of USP Tiagabine Hydrochloride RS in the Standard preparation; and RU and RS are the peak area ratios of tiagabine hydrochloride to the internal standard obtained from the Assay preparation and the Standard preparation, respectively.