Identification—
A:
The UV absorption spectrum of the solution employed for measurement of absorbance in the
Assay exhibits maxima and minima at the same wavelengths as that of a similar solution of
USP Chloroquine Phosphate RS, concomitantly measured. The ratio
A343/
A329 is between 1.00 and 1.15.
B:
To 20 mL of a dilution of Injection with water, containing about 20 mg of chloroquine hydrochloride, add 5 mL of trinitrophenol TS: a yellow precipitate is formed. Filter, wash the precipitate with water until the last washing is colorless, and dry over silica gel: the precipitate melts between 205
and 210
. [
Caution—Picrates may explode.]
C:
It responds to the tests for
Chloride 
191
.
Assay—
Transfer an accurately measured volume of Injection, equivalent to about 150 mg of chloroquine hydrochloride, to a 1000-mL volumetric flask, and dilute with water to volume. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, add 10 mL of dilute hydrochloric acid (1 in 100), and dilute with water to volume. Dissolve an accurately weighed quantity of
USP Chloroquine Phosphate RS in dilute hydrochloric acid (1 in 1000), and dilute quantitatively and stepwise with dilute hydrochloric acid (1 in 1000) to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions at the wavelength of maximum absorbance at about 343 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of C
18H
26ClN
3·2HCl in the portion of Injection taken by the formula:
15.23C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Chloroquine Phosphate RS in the Standard solution; and
AU and
AS are the absorbances of the solution from the Injection and the Standard solution, respectively.
