A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: A few drops of Injection respond to the test for Citrate 191.

0.05 M Ammonium phosphate buffer, Mobile phase, System sensitivity solution, and Chromatographic system— Prepare as directed in the Assay.

Standard solution— Use the Standard preparation, prepared as directed in the Assay.

Test solution— Use the Assay preparation, prepared as directed in the Assay.

Procedure— Separately inject equal volumes (about 20 µL) of the Test solution and the Standard solution into the chromatograph, record the chromatogram for at least 2.5 times the retention time of orphenadrine citrate, and measure all of the peak areas. Calculate the percentage of each impurity in the portion of Injection taken by the formula: in which F is the relative response factor as found in the table below; C is the concentration, in mg per mL, of USP Orphenadrine Citrate RS in the Standard solution; V is the volume, in mL, of Injection taken to prepare the Test solution; D is the labeled dose of Injection; ri is the peak area for each impurity in the Test solution; and rS is the peak area of Orphenadrine Citrate in the Standard solution: not more than 4.0% of total impurities is found.

(Official January 1, 2007)

0.05 M Ammonium phosphate buffer— Dissolve 5.8 g of monobasic ammonium phosphate in 1000 mL of water, and adjust with ammonium hydroxide or phosphoric acid to a pH of 7.9 ± 0.05.

Mobile phase— Prepare a filtered and degassed mixture of methanol, 0.05 M Ammonium phosphate buffer, and acetonitrile (9:8:3). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Orphenadrine Citrate RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.9 mg per mL.

System sensitivity solution— Dilute a volume of the Standard preparation quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.00045 mg per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 90 mg of orphenadrine citrate, 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 220-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 40. Chromatograph the Standard preparation, and record the peak areas as directed for Procedure: the column efficiency is not less than 4500 theoretical plates; the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%. Chromatograph the System sensitivity solution, and record the peak areas as directed for Procedure: the signal-to-noise ration is not less than 10.

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 peak areas for orphenadrine citrate. Calculate the quantity, in mg, of orphenadrine citrate (C18H23NO·C6H8O7) in each mL of the Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Orphenadrine Citrate 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.