Standard solution— Transfer 2.0mLof 0.100Niodine VSto a 500-mLvolumetric flask,dilute with water to volume,and mix.

Procedure— Visually examine a portion of the Injection (Test solution)in a suitable clear glass test tube against a white background:it is not pinkish and it contains no precipitate.If any yellow color is observed in the Test solution,concomitantly determine the absorbances of the Test solutionand the Standard solutionin 1-cm cells with a suitable spectrophotometer set at 460nm:the absorbance of the Test solutiondoes not exceed that of the Standard solution.

A: It responds to Identificationtest Bunder Norepinephrine Bitartrate.

B: Dilute the Injection with water to a concentration of 1mg in 5mL.To 10mLof the dilution add 2.0mLof 0.10Niodine,allow to stand for 5minutes,then add 3.0mLof 0.10Nsodium thiosulfate:the solution is colorless or has at most a slight pink or slight violet color (epinephrine and isoproterenol at the same pH,about 3.5,give a red-brown or violet color).

Mobile phase— Dissolve 1.1g of sodium 1-heptanesulfonate in 800mLof water.Add 200mLof methanol,and adjust with 1Mphosphoric acid to a pHof 3.0±0.1.Pass through a membrane filter.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Norepinephrine Bitartrate RSin freshly prepared dilute acetic acid (1in 25),and dilute quantitatively,and stepwise if necessary,to obtain a solution having a known concentration of about 0.4mg of norepinephrine bitartrate monohydrate per mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 5mg of norepinephrine,to a 25-mLvolumetric flask,add dilute acetic acid (1in 25)to volume,and mix.

System suitability preparation— Dissolve a suitable quantity of isoproterenol hydrochloride in the Standard preparationto obtain a solution containing,in each mL,0.4mg of USP Norepinephrine Bitartrate RSand 0.4mg of isoproterenol hydrochloride.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparationand the System suitability preparation,and record the peak responses as directed under Procedure:the tailing factor for the analyte peak is not more than 2.5,the resolution,R,between the norepinephrine and isoproterenol peaks is not less than 4.0,and the relative standard deviation for replicate injections is not more than 2.0%.

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 norepinephrine (C8H11NO3)in each mLof the Injection taken by the formula: in which 169.18and 337.29are the molecular weights of norepinephrine and norepinephrine bitartrate monohydrate,respectively;Cis the concentration,in mg per mL,of USP Norepinephrine Bitartrate RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.