Assay—
[NOTE—Use low-actinic flasks in preparing the solutions, and otherwise protect the solutions from unnecessary exposure to bright light. Complete the assay without prolonged interruption.
] Place a number of Tablets, equivalent to 500 mg of pyrvinium, in a 500-mL volumetric flask, and add 25 mL of water and 25 mL of acetone. Completely disintegrate the tablets by heating on the steam bath for 10 minutes with frequent mixing, allowing part of the acetone to boil off slowly. To the hot mixture add 250 mL of glacial acetic acid, and mix occasionally for 5 minutes without further heating, to dissolve the pyrvinium pamoate. Dilute with methanol to volume at room temperature, and mix. Centrifuge a portion of the mixture until a clear solution is obtained. Transfer 3 mL of the clear supernatant to a 500-mL volumetric flask, dilute with methanol to volume, and mix. Dissolve an accurately weighed quantity of
USP Pyrvinium Pamoate RS in glacial acetic acid, using 1 mL for each 3 mg taken, and dilute quantitatively and stepwise with methanol to obtain a Standard solution having a known concentration of about 9 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 505 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of pyrvinium (C
26H
28N
3+) in the portion of Tablets taken by the formula:
83.3C(0.6644AU / AS),
in which
C is the concentration, in µg per mL, of
USP Pyrvinium Pamoate RS in the Standard solution, calculated on the anhydrous basis, 0.6644 is the ratio of the molecular weight of pyrvinium to one-half the molecular weight of pyrvinium pamoate, and
AU and
AS are the absorbances of the solution from the Tablets and the Standard solution, respectively.
701
:
30 minutes.