A: Infrared Absorption 197M.

B: The retention time of the major peak in the chromatogram of the Test solution corresponds to that in the chromatogram of the Resolution solution, as obtained in the test for Limit of lamivudine enantiomer.

0.1 M Ammonium acetate solution— Dissolve about 7.7 g of ammonium acetate in water, and dilute with water to 1000 mL.

Mobile phase— Prepare a suitable mixture of 0.1 M Ammonium acetate solution and methanol (95:5), mix, filter, and degas.

Resolution solution— Dissolve an accurately weighed quantity of USP Lamivudine Resolution Mixture A RS in water to obtain a solution having a known concentration of about 0.25 mg per mL.

Test solution— Transfer about 25 mg of Lamivudine, 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 270-nm detector and a 4.6-mm × 25-cm column that contains packing L45. The column temperature is maintained at a constant temperature of between 15 and 30. The flow rate is about 1.0 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between lamivudine and lamivudine enantiomer is not less than 1.5. [note—The relative retention times are about 1.0 for lamivudine and about 1.2 for lamivudine enantiomer.]

Procedure— Inject a volume (about 10 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the responses for the major peaks. Calculate the percentage of lamivudine enantiomer in the portion of Lamivudine taken by the formula: in which rU and rS are the peak responses of lamivudine enantiomer and lamivudine, respectively: not more than 0.3% is found.

Internal standard solution— Transfer about 1 mL of 2-pentanone, accurately measured, to a 100-mL volumetric flask, dilute with a mixture of dimethyl sulfoxide and water (1:1) to volume, and mix.

Standard solution— Transfer 10 mL of Internal standard solution to a 100-mL volumetric flask. To the same flask add an accurately measured quantity of about 100 µL of each of the following: dehydrated alcohol, isopropyl acetate, methanol, and triethylamine. Dilute with a mixture of dimethyl sulfoxide and water (1:1) to volume, and mix.

Test solution— Transfer about 5 g of Lamivudine, accurately weighed, to a 100-mL volumetric flask, add 10 mL of Internal standard solution, dilute with a mixture of dimethyl sulfoxide and water (1:1) to volume, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a split injection port, a flame-ionization detector, and a 0.53-mm × 50-m column coated with a 5-µm film of phase G1. The carrier gas is hydrogen at a pressure of 5 psig. The split flow rate is about 320 mL per minute. The chromatograph is programmed as follows. Initially the temperature of the column is maintained at 70 for 3 minutes, then increased at a rate of 30 per minute to 200, and maintained at that temperature for 6.5 minutes. The injection port temperature is maintained at 150 and the detector temperature is maintained at 250.

Procedure— Separately inject equal volumes (about 0.5 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak areas. Calculate the percentage of each residual solvent in the portion of Lamivudine taken by the formula: in which C is the concentration, in mg per mL, of the respective analyte in the Standard solution; W is the weight, in g, of Lamivudine taken; and RU and RS are the peak response ratios of the respective analyte to the internal standard obtained from the Test solution and the Standard solution, respectively: not more than 0.2% of alcohol is found; not more than 0.2% of isopropyl acetate is found; not more than 0.1% of methanol is found; not more than 0.1% of triethylamine is found; and not more than 0.3% of total residual solvents is found.

0.025 M Ammonium acetate solution, Mobile phase, System suitability solution, and Chromatographic system— Proceed as directed in the Assay.

Salicylic acid solution— Dissolve an accurately weighed quantity of salicylic acid in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a concentration of about 0.625 µg per mL.

Standard solution— Use the Standard preparation, prepared as directed in the Assay.

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 10 µL) of Salicylic acid solution and the Test solution into the chromatograph, record the chromatograms, and measure all the peak responses. Calculate the percentage of salicylic acid in the portion of Lamivudine taken by the formula: in which C is the concentration, in µg per mL, of salicylic acid in the Salicylic acid solution; W is the weight, in mg, of Lamivudine taken for the Test solution; and rU and rS are the salicylic acid peak responses obtained from the Test solution and the Salicylic acid solution, respectively. Calculate the percentage of other individual impurities in the portion of Lamivudine taken by the formula: in which ri is the peak response for each impurity other than salicylic acid obtained from the Test solution; and rs is the sum of the responses for all the peaks: not more than 0.3% for any peak at a relative retention time of about 0.4 is found; not more than 0.2% for any peak at a relative retention time of about 0.9 is found; not more than 0.1% of salicylic acid is found; not more than 0.1% of any other individual impurity is found; and not more than 0.6% of total impurities is found.

0.025 M Ammonium acetate solution— Transfer about 1.9 g of ammonium acetate to a 1000-mL volumetric flask, dissolve in about 900 mL of water, adjust with acetic acid to a pH of 3.8 ± 0.2, dilute with water to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of 0.025 M Ammonium acetate solution and methanol (95:5). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Dissolve an accurately weighed quantity of USP Lamivudine Resolution Mixture B RS in Mobile phase to obtain a solution having a known concentration of about 0.25 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Lamivudine RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.25 mg per mL.

Assay preparation— Transfer about 25 mg of Lamivudine, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 277-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. The column temperature is maintained at 35. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between lamivudine and lamivudine diastereomer is not less than 1.5. [note—The relative retention times are about 1.0 for lamivudine and 0.9 for lamivudine diastereomer.] Chromatograph the Standard preparation, 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the lamivudine peaks. Calculate the quantity, in mg, of C8H11N3O3S in the portion of Lamivudine taken by the formula: in which C is the concentration, in mg per mL, of USP Lamivudine RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.