Identification, Infrared Absorption 197M
Test specimen
Place a portion of powdered Tablets, equivalent to about 50 mg of methylphenidate hydrochloride, in a 40-mL centrifuge tube, add 10 mL of chloroform, shake, and centrifuge. Filter the clear extract through a medium-sized sintered-glass funnel into a beaker, and repeat the extraction with an additional 10-mL portion of chloroform. Evaporate the combined chloroform extracts on a steam bath to dryness. Agitate the dried residue with 2 mL of acetonitrile, and filter the mixture through a small sintered-glass funnel. Wash the crystals with an additional 2 mL of acetonitrile, and dry them with the aid of suction.
Assay
Acetate buffer
Dissolve 1.64 g of anhydrous sodium acetate in 900 mL of water, adjust with acetic acid to a pH of 4.0, dilute with water to 1000 mL, and mix.
Mobile phase
Prepare a filtered and degassed mixture of methanol, acetonitrile, and
Acetate buffer (4:3:3). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Internal standard solution
Dissolve phenylephrine hydrochloride in Mobile phase to obtain a solution having a concentration of about 0.4 mg per mL.
Standard preparation
Dissolve an accurately weighed quantity of
USP Methylphenidate Hydrochloride RS in
Mobile phase, and quantitatively dilute with
Mobile phase to obtain a standard stock solution having a known concentration of about 0.2 mg per mL. Transfer 10.0 mL of this standard stock solution to a glass-stoppered, 25-mL conical flask, add 5.0 mL of
Internal standard solution, and mix.
Assay preparation
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 20 mg of methylphenidate hydrochloride, to a 100-mL volumetric flask, add 70 mL of Mobile phase, and sonicate for 15 minutes. Cool to room temperature, dilute with Mobile phase to volume, and mix. Pass a portion of this solution through a suitable membrane filter, discarding the first portion of the filtrate. [NOTEAvoid the use of glass filters. Polypropylene filters are suitable for use.] Transfer 10.0 mL of the clear filtrate to a glass-stoppered, 25-mL conical flask, add 5.0 mL of Internal standard solution, and mix.
Chromatographic system (see Chromatography 621)
The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 25-cm column that contains packing L10. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the relative retention times are about 0.8 for phenylephrine hydrochloride and 1.0 for methylphenidate hydrochloride; the resolution,
R, between the analyte and the internal standard peaks is not less than 2.0; and the relative standard deviation determined from the peak response ratios of the analyte to the internal standard for replicate injections is not more than 2.0%.
Procedure
Separately inject equal volumes (about 50 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 methylphenidate hydrochloride (C
14H
19NO
2·HCl) in the portion of Tablets taken by the formula:
100C(RU / RS),
in which
C is the concentration, in mg per mL, of
USP Methylphenidate Hydrochloride RS in the standard stock solution used to prepare the
Standard preparation; and
RU and
RS are the peak response ratios of the analyte to the internal standard obtained from the
Assay preparation and the
Standard preparation, respectively.