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.

Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C14H19NO2·HCl dissolved by employing the procedure set forth in the Assay, making any necessary volumetric adjustments.

Tolerances— Not less than 75% (Q) of the labeled amount of C14H19NO2·HCl is dissolved in 45 minutes.

(Official January 1, 2007)

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. [NOTE—Avoid 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 (C14H19NO2·HCl) in the portion of Tablets taken by the formula: 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.