A:Infrared Absorption á197Kñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that of the Standard preparationas obtained in the Assay.

Solution A— Use Buffer solutionprepared as directed in the Assay.

Solution B— Use methanol.

Diluent— Prepare a mixture of Solution Aand Solution B(76:24).

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for the Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solutions— Dissolve an accurately weighed quantity of USP Nizatidine RSquantitatively,and stepwise if necessary,in Diluent,sonicating if necessary,to obtain a solution having a known concentration of 50µg per mL(Standard solution 1).Quantitatively dilute portions of Standard solution 1with Diluentto obtain Standard solution 2and Standard solution 3having known concentrations of 25µg per mLand 15µg per mL,respectively.

Test solution— Prepare a solution of Nizatidine in Diluenthaving a concentration of about 5mg per mL.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 1mLper minute.The chromatograph is programmed as follows. Make adjustments to the composition of the Mobile phase,if necessary,to obtain a retention time of about 12minutes for the main nizatidine peak (see System Suitabilityunder Chromatography á621ñ).Chromatograph Standard solution 1,and record the peak areas as directed for Procedure:the tailing factor is not more than 2.0.

Procedure— Separately inject equal volumes (about 50µL)of Standard solution 1,Standard solution 2,Standard solution 3,and the Test solutioninto the chromatograph,and allow the Test solutionto elute for not less than three times the retention time of nizatidine.Record the chromatograms,and measure the areas for all the peaks.The sum of the peak areas,excluding the nizatidine peak area,obtained from the Test solution is not more than three times the main peak area obtained from Standard solution 2;and no single peak area obtained from the Test solutionis greater than the main peak area obtained from Standard solution 3:not more than 0.3%of any individual impurity is found;and not more than 1.5%of total impurities is found.

Buffer solution— Prepare a 0.1Msolution by dissolving 5.9g of ammonium acetate in 760mLof water.Add 1mLof diethylamine,and adjust with acetic acid to a pHof 7.5.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solutionand methanol (76:24).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Nizatidine RSin Mobile phase,sonicating if necessary,to obtain a solution having a known concentration of about 0.3mg per mL.

Assay preparation— Transfer an accurately weighed quantity of 15mg of Nizatidine to a 50-mLvolumetric flask,dissolve in Mobile phase,sonicating if necessary,dilute with Mobile phaseto volume,and mix.

Chromatographic system (seeChromatography á621ñ)— 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 1mLper minute.Chromatograph the Standard preparation,and record the peak areas as directed for Procedure:the column efficiency is not less than 1500theoretical plates;the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of C12H21N5O2S2in the portion of Nizatidine taken by the formula: in which Cis the concentration,in mg per mL,of USP Nizatidine RSin the Standard preparation;and rUand rSare the peak areas obtained from the Assay preparationand the Standard preparation,respectively.