Identification—
Dissolve about 10 mg of
USP Benztropine Mesylate RS in 50 mL of water in a separator to obtain a solution containing about 0.2 mg per mL. Transfer a volume of Injection, equivalent to about 10 mg of benztropine mesylate, to a second separator, and dilute with water to 50 mL. Separately add 2 mL of 1 N sodium hydroxide to each separator, and mix. Extract each solution with three 10-mL portions of chloroform, collecting the chloroform extracts from both solutions in separate 50-mL beakers. Evaporate both chloroform extracts with the aid of gentle heat and a current of air to dryness, and separately dissolve each residue in 1 mL of chloroform. Apply separately 1 µL of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel. Allow the applications to dry, and develop the chromatogram in a solvent system consisting of a mixture of chloroform, methanol, and a 1 in 4 solution of ammonium hydroxide (40:10:1) 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. Locate the spots on the plate by lightly spraying with
potassium iodoplatinate TS: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Assay—
0.005 M Octylamine phosphate buffer—
Transfer 0.83 mL of octylamine to a 1-liter volumetric flask, dilute with water to volume, adjust with phosphoric acid to a pH of 3.0, and pass the solution through a membrane filter.
Mobile phase—
Mix 350 mL of 0.005 M Octylamine phosphate buffer and 650 mL of acetonitrile, and degas the solution.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Benztropine Mesylate RS in water to obtain a solution having a known concentration of about 1 mg per mL.
Assay preparation—
Dilute with water an accurately measured volume of Injection, equivalent to about 10 mg of benztropine mesylate, to obtain a solution having a concentration of about 1 mg of benztropine mesylate per mL.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 259-nm detector and a 4.6-mm × 25-cm column that contains packing L7. The flow rate is about 1.3 mL per minute. Adjust the flow rate to obtain a retention time of about 7 minutes for benztropine mesylate. Chromatograph replicate injections of the
Standard preparation, and record the peak responses as directed for
Procedure: the relative standard deviation is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 25 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the peak areas for the major peaks. Calculate the quantity, in mg, of C
21H
25NO·CH
4O
3S in each mL of the Injection taken by the formula:
10(C / V)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Benztropine Mesylate RS in the
Standard preparation,
V is the volume, in mL, of Injection taken, and
rU and
rS are the peak areas obtained for benztropine mesylate from the
Assay preparation and the
Standard preparation, respectively.
