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Mobile phase— Dissolve 1.76g of sodium 1-heptanesulfonate in 800mLof water.Add 200mLof methanol,and adjust with 1Mphosphoric acid to a pHof 3.0±0.1.Pass the solution through a membrane filter having a 1-µm or finer porosity.

Standard preparation— Dissolve an accurately weighed quantity of USP Isoproterenol Hydrochloride RSin freshly prepared sodium bisulfite solution (1in 1000)to obtain a solution having a known concentration of about 20µg per mL.

Resolution solution— Prepare a solution of epinephrine bitartrate in freshly prepared Mobile phasecontaining 1.0%of sodium bisulfite,having a concentration of about 200µg per mL.Mix 2.0mLof this solution and 18.0mLof the Standard preparation.

Assay preparation— Quantitatively dilute an accurately measured volume of Injection with freshly prepared sodium bisulfite solution (1in 1000)to obtain a solution having a concentration of about 20µg per mL.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 4-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 standard deviation for replicate injections is not more than 1.5%.Chromatograph the Resolution solution:the relative retention times are about 0.55for epinephrine and 1.0for isoproterenol;the resolution,R,for epinephrine and isoproterenol is not less than 3.5;and the tailing factors for the epinephrine and isoproterenol peaks are not more than 2.5.

Procedure— Separately inject equal volumes (about 100µL)of the Standard preparationand the Assay preparation,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of isoproterenol hydrochloride (C11H17NO3·HCl)in each mLof the Injection taken by the formula: in which Cis the concentration,in µg per mL,of USP Isoproterenol Hydrochloride RSin the Standard preparation;Lis the labeled quantity,in µg per mL,of isoproterenol hydrochloride in the Injection;Dis the concentration,in µg per mL,of isoproterenol hydrochloride in the Assay preparation,on the basis of the labeled quantity in each mLand the extent of dilution;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.