A: The IRabsorption spectrum of a potassium bromide dispersion of it,previously dried,exhibits maxima only at the same wavelengths as that of a similar preparation of USP Cimetidine RS.

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

Mobile phase— Mix 240mLof methanol,0.3mLof phosphoric acid (85%),940mg of sodium 1-hexanesulfonate,and sufficient water to make 1liter.Filter before use.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Prepare a solution of USP Cimetidine RSin Mobile phasehaving a concentration of 0.80µg per mL.

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

Chromatographic system (see Chromatography á621ñ)—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 2.0mLper minute.Chromatograph the Standard preparation,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 50µL)of the Standard preparationand the Test preparationinto the chromatograph,record the chromatograms,and measure the peak responses.The sum of all the peak responses,excluding the cimetidine response,from the Test preparationis not more than 5times the cimetidine response from the Standard preparation,and no single peak response is greater than that of the cimetidine response from the Standard preparation.

Mobile phase— Transfer 200mLof methanol and 0.3mLof phosphoric acid to a 1000-mLvolumetric flask,dilute with water to volume,mix,and filter.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

Assay preparation— Transfer an accurately weighed quantity of about 100mg of Cimetidine to a 250-mLvolumetric flask,add 50mLof methanol to dissolve the specimen,dilute with water to volume,and mix.Transfer 5.0mLof this solution to a 200-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—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 2.0mLper 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 1000theoretical plates;and the relative standard deviation of the response for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of C10H16N6Sin the portion of Cimetidine taken by the formula: in which Cis the concentration,in µg per mL,of USP Cimetidine RSin the Standard preparation;and rUand rSare the Cimetidine peak responses obtained from the Assay preparationand the Standard preparation,respectively.