Identification—
Place 1 mL of Injection in a 125-mL separator, and add 1 N sodium hydroxide dropwise until the solution becomes opaque white. Extract with 50 mL of ether, wash the ether extract with 25 mL of water, and discard the washing. Filter the ether extract through a layer of anhydrous sodium sulfate into a beaker, evaporate the filtrate by means of a stream of nitrogen to complete dryness, and dry at 100
for 3 hours: the methotrimeprazine so obtained responds to
Identification test
A under
Methotrimeprazine.
Assay—
20% Phosphoric acid—
Transfer 23.5 mL of 85% phosphoric acid into a 100-mL volumetric flask containing water, and dilute with water to volume.
Mobile phase—
Prepare a filtered and degassed mixture of water, acetonitrile,
20% Phosphoric acid, and triethylamine by using the following procedure. Add 20 mL of
20% Phosphoric acid to 450 mL of water, to this solution add 5 mL of triethylamine, and adjust with 1 N sodium hydroxide to a pH of 3.0. Add 500 mL of acetonitrile, and dilute with water to 1000 mL. Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Methotrimeprazine RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 0.1 mg per mL.
System suitability preparation—
Dissolve or add suitable quantities of 1% benzyl alcohol in
Mobile phase and
USP Methotrimeprazine RS in
Mobile phase to obtain a solution containing about 2.0 and 0.1 mg per mL, respectively.
Assay preparation—
Transfer an accurately measured amount of Injection, equivalent to about 20 mg of methotrimeprazine, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L7. The flow rate is about 1 mL per minute. Chromatograph the
System suitability preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between benzyl alcohol and methotrimeprazine is not less than 4.0; and the tailing factor is not more than 1.2. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the relative standard deviation for replicate injections is not more than 1.5%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of methotrimeprazine (C
19H
24N
2OS) in the portion of Injection taken by the formula:
200C(rU/rS),
in which
C is the concentration, in mg per mL, of
USP Methotrimeprazine RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
