Identification—
A:
The UV absorption spectrum of the solution employed for measurement of absorbance in the
Assay exhibits maxima and minima at the same wavelengths as that of the Standard solution.
B:
Transfer a portion of the contents of Capsules, equivalent to about 20 mg of trimethobenzamide hydrochloride, to a suitable vessel, dissolve in 15 mL of 0.1 N hydrochloric acid, and filter. Transfer the filtrate to a separator, and add 5 mL of 1 N sodium hydroxide. Extract with 15 mL of chloroform, filtering the chloroform extract through anhydrous sodium sulfate into a suitable vessel, and evaporate to dryness. Allow to cool to room temperature, add a small portion of ether, and evaporate at room temperature to dryness. Dry the residue at 60
for 1 hour: the IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Trimethobenzamide Hydrochloride RS.
C:
Place a portion of the contents of Capsules, equivalent to about 25 mg of trimethobenzamide hydrochloride, in a 10-mL volumetric flask, add methanol to volume, mix, and filter: the filtrate so obtained responds to 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.
Dissolution 711—
Medium:
water; 900 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
21H
28N
2O
5·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 258 nm of filtered portions of the solution under test, suitably diluted with
Medium, if necessary, in comparison with a Standard solution having a known concentration of
USP Trimethobenzamide Hydrochloride RS in the same
Medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C21H28N2O5·HCl is dissolved in 45 minutes.
Assay—
Transfer, as completely as possible, the contents of not less than 20 Capsules to a suitable tared container, and determine the average weight per Capsule. Mix the combined contents, and transfer an accurately weighed portion of the powder, equivalent to about 50 mg of trimethobenzamide hydrochloride, to a 100-mL volumetric flask. Add 50 mL of dilute hydrochloric acid (1 in 120), shake the mixture for several minutes, then add dilute hydrochloric acid (1 in 120) to volume, and mix. Filter through small retentive filter paper, discarding the first 20 mL of the filtrate. Transfer 4.0 mL of the subsequent filtrate to a 100-mL volumetric flask, add dilute hydrochloric acid (1 in 120) to volume, 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 the portion of Capsules taken by the formula:
2.5C(AU / AS),
in which
C is the concentration, in µg per mL, of USP Trimethobenzamide RS in the Standard solution, and
AU and
AS are the absorbances of the solution from the Capsules and the Standard solution, respectively.
