Identification—
The absorption spectrum,between 300nm and 600nm,of the solution employed for measurement of absorbance in the
Assayexhibits 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 5mLof Oral Suspension,freshly mixed and free from air bubbles,to a 250-mLvolumetric flask.Complete the transfer by rinsing the pipet with 10mLof methanol.Add 100mLof glacial acetic acid,and mix to dissolve the pyrvinium pamoate.Dilute this solution with methanol to volume,and mix.Transfer 3mLof the resulting solution to a 100-mLvolumetric flask,dilute with methanol to volume,and mix.Dissolve an accurately weighed quantity of
USP Pyrvinium Pamoate RSin glacial acetic acid,using 4mLfor each 3mg taken,and dilute quantitatively and stepwise with methanol to obtain a Standard solution having a known concentration of about 9µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 505nm,with a suitable spectrophotometer,using methanol as the blank.Calculate the quantity,in g per 100mL,of pyrvinium (C
26H
28N
3+)in the Oral Suspension taken by the formula:
0.1667C(0.6644AU/AS),
in which
Cis the concentration,in µg per mL,of
USP Pyrvinium Pamoate RSin the Standard solution,calculated on the anhydrous basis;0.6644is the ratio of the molecular weight of pyrvinium to one-half the molecular weight of pyrvinium pamoate;and
AUand
ASare the absorbances of the solution prepared from the Oral Suspension and the Standard solution,respectively.