Identification—
A:
Transfer a measured volume of Oral Solution, equivalent to about 50 mg of nortriptyline hydrochloride, to a suitable separator, and render the solution distinctly alkaline (to a pH of 11 or above as indicated by pH indicator paper) by the dropwise addition of 1 N sodium hydroxide. Extract with 15 mL of chloroform, and filter the chloroform extract through about 2 g of anhydrous sodium sulfate that has been previously washed with chloroform. Evaporate the chloroform extract with the aid of heat and a current of air to dryness, and dissolve the residue in 0.5 mL of chloroform: the IR absorption spectrum of this solution exhibits maxima only at the same wavelengths as that of a Standard solution obtained by dissolving 50 mg of
USP Nortriptyline Hydrochloride RS in 25 mL of water and proceeding as directed for the test specimen.
B:
It responds to the tests for
Chloride 
191
, when tested as specified for alkaloidal hydrochlorides.
Assay—
Transfer an accurately measured volume of Oral Solution, equivalent to about 10 mg of nortriptyline, to a 125-mL separator. Add 20 mL of water, mix, and render the solution distinctly alkaline (to a pH of 11 or above as indicated by pH indicator paper) by the dropwise addition of sodium hydroxide solution (1 in 2). Extract the nortriptyline with four 25-mL portions of chloroform, filtering each extract into a 250-mL beaker through about 12 g of anhydrous sodium sulfate previously washed with 25 mL of chloroform. Rinse the sodium sulfate with four 5-mL portions of chloroform, and collect the rinsings in the beaker. Evaporate the combined chloroform solution with the aid of heat and a current of air to about 10 mL. Transfer the contents of the beaker with the aid of chloroform to a 200-mL volumetric flask. Evaporate the chloroform with the aid of air alone to dryness.
[Caution—Do not use heat.
] Dissolve the residue in 1.7 mL of hydrochloric acid, dilute with water to volume, and mix. Transfer 10.0 mL of the solution to a 50-mL volumetric flask, dilute with water to volume, and mix to obtain the
Assay preparation. Concomitantly determine the absorbances of the
Assay preparation and a Standard solution of
USP Nortriptyline Hydrochloride RS in water having a known concentration of about 11.4 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 239 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of C
19H
21N in the portion of Oral Solution taken by the formula:
(263.38/299.85)(C)(AU / AS),
in which 263.38 and 299.85 are the molecular weights of nortriptyline and nortriptyline hydrochloride, respectively;
C is the concentration, in µg per mL, of
USP Nortriptyline Hydrochloride RS in the Standard solution; and
AU and
AS are the absorbances of the
Assay preparation and the Standard solution, respectively.
