Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 2:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
18H
26ClN
3·2H
3PO
4 dissolved from UV absorbances at the wavelength of maximum absorbance at about 343 nm of filtered portions of the solution under test, suitably diluted with
Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of
USP Chloroquine Phosphate RS in the same medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C18H26ClN3·2H3PO4 is dissolved in 45 minutes.
Assay—
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 800 mg of chloroquine phosphate, to a 200-mL volumetric flask, add about 100 mL of water, and shake by mechanical means for about 20 minutes. Add water to volume, mix, and filter, discarding the first 50 mL of the filtrate. Pipet 50 mL of the clear filtrate into a 250-mL separator, add 5 mL of 6 N ammonium hydroxide, agitate, and extract the liberated chloroquine with five 25-mL portions of chloroform. Wash the combined chloroform extracts with 10 mL of water, and extract the water washing with 10 mL of chloroform. Evaporate the combined chloroform extracts on a steam bath to about 10 mL, then add 50 mL of dilute hydrochloric acid (1 in 250), and continue heating on the steam bath until the odor of chloroform is no longer perceptible. Transfer the solution to a 200-mL volumetric flask, wash the evaporating vessel with portions of dilute hydrochloric acid (1 in 1000), adding the washings to the volumetric flask, add more of the same dilute hydrochloric acid to volume, and mix. Dilute this solution quantitatively and stepwise with dilute hydrochloric acid (1 in 1000) to obtain an estimated concentration of 10 µg per mL. Dissolve an accurately weighed quantity of
USP Chloroquine Phosphate RS in dilute hydrochloric acid (1 in 1000), and dilute quantitatively and stepwise with the same dilute hydrochloric acid to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 343 nm, with a suitable spectrophotometer, using dilute hydrochloric acid (1 in 1000) as the blank. Calculate the quantity, in mg, of C
18H
26ClN
3·2H
3PO
4 in the portion of Tablets taken by the formula:
80C(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 Tablets and the Standard solution, respectively.
