A: Infrared Absorption 197K.

B: The UV absorption spectrum of a solution (1 in 80,000) in 0.1 N sulfuric acid exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Cimetidine RS, concomitantly measured.

Mobile phase— Mix 240 mL of methanol, 0.3 mL of phosphoric acid (85%), 940 mg of sodium 1-hexanesulfonate, and sufficient water to make 1 L. Filter before use. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Prepare a solution of USP Cimetidine RS in Mobile phase having a concentration of 0.80 µg per mL.

Test solution— Transfer 100.0 mg of Cimetidine, accurately weighed, to a 250-mL volumetric flask, dissolve in about 50 mL of Mobile phase, and dilute with Mobile phase to volume. Mix, sonicate for 15 minutes, and mix again.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 2.0 mL per minute. Chromatograph the Standard solution, and record the peak response as directed for Procedure: the capacity factor, k ¢, is not less than 3.0; the number of theoretical plates, n, is not less than 2000; and the relative standard deviation of the response for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of each impurity in the portion of Cimetidine taken by the formula: in which CS is the concentration, in µg per mL, of cimetidine in the Standard solution, the multiplier of 0.001 is for conversion of µg per mL to mg per mL; CU is the concentration, in mg per mL, of Cimetidine in the Test solution; rU is the peak response for each impurity obtained from the Test solution; and rS is the response of the cimetidine peak obtained from the Standard solution: not more than 0.2% of any single impurity is found, and not more than 1.0% of total impurities is found.

Mobile phase— Transfer 200 mL of methanol and 0.3 mL of phosphoric acid to a 1000-mL volumetric flask, dilute with water to volume, mix, and filter. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Cimetidine RS in a mixture of water and methanol (4:1) to obtain a stock solution having a known concentration of about 0.4 mg per mL by initially dissolving the Reference Standard in one part of methanol and diluting the methanolic solution quantitatively with about 4 parts of water to volume in a volumetric flask. Transfer 5.0 mL of this stock solution to a 200-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a solution having a known concentration of about 10 µg per mL.

Assay preparation— Transfer an accurately weighed quantity of about 100 mg of Cimetidine to a 250-mL volumetric flask, add 50 mL of methanol to dissolve the specimen, dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a 200-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 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the capacity factor, k¢, is not less than 0.6; the column efficiency determined from the analyte peak is not less than 1000 theoretical plates; and the relative standard deviation of the response for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of C10H16N6S in the portion of Cimetidine taken by the formula: in which C is the concentration, in µg per mL, of USP Cimetidine RS in the Standard preparation; and rU and rS are the Cimetidine peak responses obtained from the Assay preparation and the Standard preparation, respectively.