Identification—
Transfer a volume of Injection to a suitable container, and dilute if necessary, with dilute methanol (1 in 5) to obtain a test solution having a known concentration of 1.6 mg per mL. Prepare a Standard solution of
USP Dopamine Hydrochloride RS in dilute methanol (1 in 5) having the same concentration as the test solution. The test solution so obtained responds to the
Thin-layer Chromatographic Identification Test 
201
, a mixture of
n-butyl alcohol, glacial acetic acid, and water (4:1:1) being used as the developing solvent and 5 µL each of the test solution and Standard solution being applied to the thin-layer chromatographic plate.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of 0.005
M sodium 1-octanesulfonate in 1% glacial acetic acid and acetonitrile (87:13). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve a suitable quantity of
USP Dopamine Hydrochloride RS, accurately weighed, in
Mobile phase to obtain a solution having a concentration of about 1.6 mg per mL. Pipet 10 mL of this solution into a 100-mL volumetric flask, dilute with
Mobile phase to volume, and mix to obtain a
Standard preparation having a known concentration of about 0.16 mg of dopamine hydrochloride per mL.
System suitability solution—
Prepare a solution of benzoic acid in methanol containing about 20 mg per mL. Dilute 1 volume of this solution with 3 volumes of the
Mobile phase to obtain a solution having a final concentration of about 5 mg per mL. Transfer 10.0 mL of this solution and 10.0 mL of a Standard solution containing 1.6 mg of
USP Dopamine Hydrochloride RS per mL to a 100-mL volumetric flask, dilute with
Mobile phase to volume, and mix.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 16 mg of dopamine hydrochloride, to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 280-nm detector and a 4-mm × 30-cm column packed with packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
System suitability solution, and record the peak responses as directed under
Procedure: the resolution,
R, between benzoic acid and dopamine hydrochloride is not less than 4.0. Chromatograph the
Standard preparation, and record the peak responses as directed under
Procedure: the relative standard deviation for replicate injections is not more than 3.0%.
Procedure—
Separately inject equal volumes (about 40 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 C
8H
11NO
2·HCl in each mL of the Injection taken by the formula:
(100C / V)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Dopamine Hydrochloride RS in the
Standard preparation; V is the volume, in mL, of Injection taken; and
rU and
rS are the responses of dopamine hydrochloride obtained from the
Assay preparation and the
Standard preparation, respectively.
