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.

C: It responds to the test for Sulfate 191.

Phosphate buffer, Mobile phase, and System suitability solution— Proceed as directed in the Assay.

Standard solution— Dissolve accurately weighed quantities of USP Clopidogrel Bisulfate RS, USP Clopidogrel Related Compound A RS, USP Clopidogrel Related Compound B RS, and USP Clopidogrel Related Compound C RS in methanol, and dilute with methanol to obtain a solution having known concentrations of about 20 µg per mL, 40 µg per mL, 120 µg per mL, and 200 µg per mL, respectively. Transfer 5 mL of this solution to a 200-mL volumetric flask, and dilute with Mobile phase to volume, and mix to obtain a solution having final concentrations of about 0.5 µg per mL, 1 µg per mL, 3 µg per mL, and 5 µg per mL, respectively.

Test solution— Transfer about 100 mg of Clopidogrel Bisulfate, accurately weighed, to a 200-mL volumetric flask, dissolve in 5 mL of methanol and dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and 4.6-mm × 15-cm column that contains packing L57. The flow rate is about 1.0 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.5 for clopidogrel related compound A, 0.8 and 1.2 for the two enantiomers of clopidogrel related compound B, 1.0 for clopidogrel, and 2.0 for clopidogrel related compound C; and the resolution, R, between clopidogrel and the first enantiomer of clopidogrel related compound B is greater than 2.5. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 15% for each peak.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the areas for all the peaks. Calculate the percentage of clopidogrel related compound A and clopidogrel related compound C in the portion of Clopidogrel Bisulfate taken by the formula: in which CA is the concentration, in mg per mL, of the relevant clopidogrel related compound in the Standard solution; CT is the concentration, in mg per mL, of Clopidogrel Bisulfate in the Test solution; rU is the peak response for the relevant clopidogrel related compound obtained from the Test solution; and rS is the peak response for the relevant clopidogrel related compound obtained from the Standard solution.

Phosphate buffer— Dissolve 1.36 g of monobasic potassium phosphate in about 500 mL of water, and dilute with water to 1000 mL.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate buffer and acetonitrile (75:25). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Clopidogrel Bisulfate RS in methanol to obtain a solution having a known concentration of about 1.0 mg of clopidogrel bisulfate per mL. Dilute a suitable portion of this solution, accurately measured, with Mobile phase to obtain a solution having a known concentration of about 0.1 mg per mL.

System suitability solution— Dissolve accurately weighed quantities of USP Clopidogrel Bisulfate RS and USP Clopidogrel Related Compound B RS in methanol, and quantitatively dilute with methanol to obtain a solution having concentrations of about 100 µg per mL and 200 µg per mL, respectively. Transfer 5 mL of this solution to a 200-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Assay preparation— Transfer about 100 mg of Clopidogrel Bisulfate, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with methanol to volume, and mix. Pipet 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 15-cm column that contains packing L57. The flow rate is about 1.0 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.8 and 1.2 for enantiomers of clopidogrel related compound B, respectively, and 1.0 for clopidogrel; and the resolution, R, between clopidogrel and the first enantiomer of clopidogrel related compound B is greater than 2.5. Chromatograph the Standard preparation: the relative standard deviation for replicate injections determined from clopidogrel bisulfate is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for all the peaks. Calculate the quantity, in mg, of C16H16ClNO2S·H2SO4 in the portion of Clopidogrel Bisulfate taken by the formula: in which C is the concentration, in mg per mL, of USP Clopidogrel Bisulfate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.