Standard solution— Transfer 2.0 mL of 0.100 N iodine VS to a 500-mL volumetric 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 solution and the Standard solution in 1-cm cells with a suitable spectrophotometer set at 460 nm: the absorbance of the Test solution does not exceed that of the Standard solution.

A: It responds to Identification test B under Norepinephrine Bitartrate.

B: Dilute the Injection with water to a concentration of 1 mg in 5 mL. To 10 mL of the dilution add 2.0 mL of 0.10 N iodine, allow to stand for 5 minutes, then add 3.0 mL of 0.10 N sodium 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).

(Official January 1, 2007)

Mobile phase— Dissolve 1.1 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 through a membrane filter. Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

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

Chromatographic system (see Chromatography 621)—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 2 mL per minute. Chromatograph the Standard preparation and 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 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of norepinephrine (C8H11NO3) in each mL of the Injection taken by the formula: in which 169.18 and 337.29 are the molecular weights of norepinephrine and norepinephrine bitartrate monohydrate, respectively; C is the concentration, in mg per mL, of USP Norepinephrine Bitartrate RS in the Standard preparation; V is the volume, in mL, of Injection taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.