Identification—
A:
Standard solution—Dissolve 20 mg of
USP Maprotiline Hydrochloride RS in 1.0 mL of methanol.
Test solution—
Transfer a portion of powdered Tablets, equivalent to about 100 mg of maprotiline hydrochloride, to a glass-stoppered centrifuge tube. Add 5.0 mL of methanol to the tube, sonicate for 10 minutes, shake by mechanical means for 10 minutes, and centrifuge.
Procedure—
In a suitable chromatographic chamber (see
Chromatography 
621
), place a volume of a solvent system consisting of a mixture of secondary butyl alcohol, ethyl acetate, and 2 N ammonium hydroxide (6:3:1) sufficient to develop a chromatogram. Place a beaker containing 25 mL of ammonium hydroxide in the bottom of the chamber, and allow it to equilibrate for 1 hour. Apply 5-µL portions of the
Test solution and the
Standard solution to a suitable thin-layer chromatographic plate, coated with a 0.25-mm layer of chromatographic silica gel that has been prewashed with chloroform by allowing chloroform to travel the full length of the plate and dried at 100
for 30 minutes, and allow the spots to dry. Develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate, remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Expose the plate to hydrogen chloride vapor for 30 minutes, expose it to a high-intensity UV light irradiator (1000 to 1600 watts)
[Caution—UV irradiators emit UV radiation that is harmful to eyes and skin.
] for 5 minutes, and compare the chromatograms under long-wavelength UV light: the
RF value of the principal spot obtained from the
Test solution corresponds to that obtained from the
Standard solution.
B:
The retention time of the major peak in the chromatogram of the
Assay preparation corresponds to that of the
Standard preparation, as obtained in the
Assay.
Dissolution 711—
Medium:
dilute hydrochloric acid (7 in 1000); 900 mL.
Apparatus 2:
50 rpm.
Time:
60 minutes.
Procedure—
Determine the amount of C
20H
23N·HCl dissolved from UV absorbances, using the difference between the absorbance maximum at about 272 nm and the absorbance minimum at about 268 nm, of filtered portions of the solution under test, suitably diluted with dilute hydrochloric acid (7 in 1000), in comparison with a Standard solution having a known concentration of
USP Maprotiline Hydrochloride RS in the same
Medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C20H23N·HCl is dissolved in 60 minutes.
Assay—
Mobile phase—
Dissolve 4 g of tetramethylammonium chloride in 495 mL of water, add 500 mL of acetonitrile and 1 mL of phosphoric acid, mix, filter, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Transfer an accurately weighed quantity of
USP Maprotiline Hydrochloride RS to a suitable volumetric flask, and prepare a solution having a known concentration of about 0.75 mg per mL in a mixture of water, methanol, and 0.1 N hydrochloric acid (80:10:10) by sonicating the Reference Standard in the methanol and 0.1 N hydrochloric acid for 5 minutes to dissolve, diluting with water to volume, and mixing.
Assay preparation—
Transfer not fewer than 15 Tablets to a 500-mL volumetric flask, add 100 mL of 0.1 N hydrochloric acid, sonicate, and shake occasionally for 5 minutes to disintegrate the Tablets. Add 100 mL of methanol, shake, and sonicate for 5 minutes. Dilute with water to volume, mix, and centrifuge. Dilute a portion of the supernatant quantitatively, and stepwise if necessary, with water to obtain a solution having a concentration of about 0.75 mg per mL. [NOTE—Filtration through commonly available filters may result in unsatisfactory drug adsorption.]
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 272-nm detector and an 8-mm × 10-cm column that contains 10-µm packing L10. The flow rate is about 2.0 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency, determined from the analyte peak, is not less than 1500 theoretical plates; the tailing factor is not more than 2.0; and the relative standard deviation of the major peak response from replicate injections is not more than 2.0%.
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 areas for the major peaks. Calculate the quantity, in mg, of C
20H
23N·HCl in the portion of Tablets taken by the formula:
(L / D)C(rU / rS),
in which
L is the labeled amount, in mg, of maprotilene hydrochloride in each Tablet;
D is the concentration, in mg per mL, of maprotilene hydrochloride in the
Assay preparation, based on the labeled quantity per Tablet and the extent of dilution;
C is the concentration, in mg per mL, of
USP Maprotiline Hydrochloride RS in the
Standard preparation; and
rU and
rS are the maprotilene peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
