pH3.1Tetramethylammonium phosphate buffer— Dissolve 1.38g of monobasic sodium phosphate and 2.0mLof 25%tetra-methylammonium hydroxide solution in methanol in 800mLof water,adjust with phosphoric acid to a pHof 3.1±0.1,dilute with water to 1000mL,and mix.

Mobile phase— Transfer 15mLof tetrahydrofuran and 75mLof acetonitrile to a 1000-mLvolumetric flask,and dilute with pH3.1Tetramethylammonium phosphate bufferto volume.

Standard preparation— Dissolve an accurately weighed quantity of USP Bretylium Tosylate RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.2mg per mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 10mg of bretylium tosylate,to a 50-mLvolumetric flask,dilute with water to 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 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for tosylate and 1.0for bretylium;the resolution,R,between the bretylium and tosylate peaks is not less than 3.0;and the relative standard deviation for replicate injections is not more than 1.4%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C18H24BrNO3Sin each mLof the Injection taken by the formula: in which Cis the concentration,in mg per mL,of USP Bretylium Tosylate RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and rUand rSare the bretylium peak responses obtained from the Assay preparationand the Standard preparation,respectively.