USP Reference standards 
11
—
USP Promazine Hydrochloride RS.
NOTE—Throughout the following procedures, protect test or assay specimens, the Reference Standard, and solutions containing them, by conducting the procedures without delay, under subdued light, or using low-actinic glassware.
Assay—
[NOTE—Use low-actinic glassware.
] Transfer a volume of Syrup, equivalent to about 10 mg of promazine hydrochloride, to a 250-mL separator. Proceed as directed in the
Assay under
Promazine Hydrochloride Oral Solution, beginning with “Add water to adjust the volume to about 45 mL.” Calculate the quantity, in mg, of C
17H
20N
2S·HCl in each mL of the Syrup taken by the formula:
(0.25C / V)(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Promazine Hydrochloride RS in the Standard solution,
V is the volume, in mL, of Syrup taken, and
AU and
AS are the absorbances of the solution from the Syrup and the Standard solution, respectively.
