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 an accurately measured volume of Oral Solution, or a quantitative dilution of it in water, equivalent to about 10 mg of promazine hydrochloride, to a 250-mL separator. Add water to adjust the volume to about 45 mL, add 3 mL of sodium hydroxide solution (1 in 10), mix, and extract the promazine with five 25-mL portions of ether. Wash the combined ether extracts with 25 mL of water, and discard the aqueous washings. Extract the combined ether extract with one 50-mL and four 25-mL portions of 0.1 N hydrochloric acid. Filter the acid extracts through a pledget of cotton washed with 0.1 N hydrochloric acid into a 250-mL volumetric flask, dilute with the same acid to volume, and mix. Without delay, concomitantly determine the absorbances of this solution and of a Standard solution of
USP Promazine Hydrochloride RS in the same medium having a known concentration of about 40 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 301 nm, with a suitable spectrophotometer, using 0.1 N hydrochloric acid as the blank. Calculate the quantity, in mg, of C
17H
20N
2S·HCl in each mL of the Oral Solution 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 Oral Solution taken, and
AU and
AS are the absorbances from the assay solution and the Standard solution, respectively.
