Identification—
The absorption spectrum, between 300 nm and 600 nm, 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 Pyrvinium Pamoate RS, concomitantly measured.
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.
] Using a pipet calibrated “to contain,” transfer 5 mL of Oral Suspension, freshly mixed and free from air bubbles, to a 250-mL volumetric flask. Complete the transfer by rinsing the pipet with 10 mL of methanol. Add 100 mL of glacial acetic acid, and mix to dissolve the pyrvinium pamoate. Dilute this solution with methanol to volume, and mix. Transfer 3 mL of the resulting solution to a 100-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 4 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 g per 100 mL, of pyrvinium (C
26H
28N
3+) in the Oral Suspension taken by the formula:
0.1667C(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 prepared from the Oral Suspension and the Standard solution, respectively.
905
—