A: Dilute a volume of Injection, equivalent to about 1.25 mg of anileridine, with water to 5 mL, and add 2 mL of a 1 in 100 solution of p-dimethylaminobenzaldehyde in alcohol: a yellow color develops immediately.

B: A volume of Injection, diluted with water to a concentration of about 25 mg of anileridine in 1000 mL, exhibits absorbance maxima at 234 ± 1 and 285 ± 2 nm.

Standard preparation— [note—Prepare on the day of the assay.] Dissolve an accurately weighed quantity of USP Anileridine Hydrochloride RS in 0.1 N hydrochloric acid, and quantitatively dilute with the same solvent to obtain a solution having a known concentration of about 250 µg per mL. (Each mg of anileridine hydrochloride is equivalent to 0.8286 mg of anileridine.)

Assay preparation— Transfer to a 500-mL volumetric flask an accurately measured volume of Injection, equivalent to about 100 mg of anileridine, dilute with 0.1 N hydrochloric acid to volume, and mix.

Procedure— Transfer 5.0 mL each of the Standard preparation, the Assay preparation, and 0.1 N hydrochloric acid to provide the blank to separate 200-mL volumetric flasks. To each flask add 25 mL of water, 5 mL of 1 N hydrochloric acid, and 5 mL of sodium nitrite solution (1 in 1000), and mix. Allow to stand for 2 minutes, then add to each flask 5 mL of ammonium sulfamate solution (1 in 200), and mix. Allow to stand for 3 minutes, then add 5 mL of N-(1-naphthyl)ethylenediamine dihydrochloride solution (1 in 1000), and mix. Allow to stand for 1 hour, dilute with water to volume, and mix. Determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 560 nm, with a suitable spectrophotometer, using the reagent blank to set the instrument. Calculate the quantity, in mg, of anileridine (C22H28N2O2) in each mL of the Injection taken by the formula: in which 352.48 and 425.40 are the molecular weights of anileridine and anileridine hydrochloride, respectively; C is the concentration, in µg per mL, of USP Anileridine Hydrochloride RS in the Standard preparation; V is the volume, in mL, of Injection taken; and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.