Identification—
A:
It meets the requirements of Identification test A under Trimethobenzamide Hydrochloride Capsules.
B:
Transfer a volume of Injection, equivalent to about 100 mg of trimethobenzamide hydrochloride, to a separator containing 20 mL of water. Add 2 mL of 1 N sodium hydroxide, and proceed as directed in
Identification test
B under
Trimethobenzamide Hydrochloride Capsules, beginning with “Extract with 15 mL of chloroform.”
C:
Dilute a portion of Injection quantitatively and stepwise with methanol to obtain a solution containing 2.5 mg of trimethobenzamide hydrochloride per mL: this solution meets the requirements of the
Thin-layer Chromatographic Identification Test 
201
, a solvent system consisting of a mixture of ethyl acetate, alcohol, and ammonium hydroxide (90:10:5) being used.
Assay—
Transfer to a suitable separator an accurately measured volume of Injection, equivalent to about 200 mg of trimethobenzamide hydrochloride. Add 5 mL of water and 3 mL of dilute hydrochloric acid (1 in 12), and extract with four 20-mL portions of ether, collecting the ether extracts in a second separator, and transferring the aqueous layer to a 500-mL volumetric flask. Wash the combined ether extracts with one 20-mL portion of water, transfer the aqueous layer to the 500-mL volumetric flask, dilute with water to volume, and mix. Dilute 5.0 mL of the solution with dilute hydrochloric acid (1 in 120) to 100.0 mL, and mix. Concomitantly determine the absorbances of this solution and a Standard solution of
USP Trimethobenzamide Hydrochloride RS in the same medium having a known concentration of about 20 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 258 nm, with a suitable spectrophotometer, using dilute hydrochloric acid (1 in 120) as the blank. Calculate the quantity, in mg, of C
21H
28N
2O
5·HCl in each mL of the Injection taken by the formula:
(10C / V)(AU / AS),
in which
C is the concentration, in µg per mL, of USP Trimethobenzamide RS in the Standard solution,
V is the volume, in mL, of Injection taken, and
AU and
AS are the absorbances of the solution from the Injection and the Standard solution, respectively.
