Mobile phase— Dissolve 1.76 g of sodium 1-heptanesulfonate in 800 mL of water. Add 200 mL of methanol, and adjust with 1 M phosphoric acid to a pH of 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 RS in freshly prepared sodium bisulfite solution (1 in 1000) to obtain a solution having a known concentration of about 20 µg per mL.

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

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

Chromatographic system (see Chromatography 621)— 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 2 mL per 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 0.55 for epinephrine and 1.0 for 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 100 µL) of the Standard preparation and the Assay preparation, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of isoproterenol hydrochloride (C11H17NO3·HCl) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Isoproterenol Hydrochloride RS in the Standard preparation; L is the labeled quantity, in µg per mL, of isoproterenol hydrochloride in the Injection; D is the concentration, in µg per mL, of isoproterenol hydrochloride in the Assay preparation, on the basis of the labeled quantity in each mL and the extent of dilution; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.