Test specimen— Place a portion of powdered Tablets,equivalent to about 50mg of methylphenidate hydrochloride,in a 40-mLcentrifuge tube,add 10mLof 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-mLportion of chloroform.Evaporate the combined chloroform extracts on a steam bath to dryness.Agitate the dried residue with 2mLof acetonitrile,and filter the mixture through a small sintered-glass funnel.Wash the crystals with an additional 2mLof acetonitrile,and dry them with the aid of suction.

Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

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 45minutes.

Acetate buffer— Dissolve 1.64g of anhydrous sodium acetate in 900mLof water,adjust with acetic acid to a pHof 4.0,dilute with water to 1000mL,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 Suitabilityunder Chromatography á621ñ).

Internal standard solution— Dissolve phenylephrine hydrochloride in Mobile phaseto obtain a solution having a concentration of about 0.4mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Methylphenidate Hydrochloride RSin Mobile phase,and quantitatively dilute with Mobile phaseto obtain a standard stock solution having a known concentration of about 0.2mg per mL.Transfer 10.0mLof this standard stock solution to a glass-stoppered,25-mLconical flask,add 5.0mLof Internal standard solution,and mix.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 20mg of methylphenidate hydrochloride,to a 100-mLvolumetric flask,add 70mLof Mobile phase,and sonicate for 15minutes.Cool to room temperature,dilute with Mobile phaseto 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 10.0mLof the clear filtrate to a glass-stoppered,25-mLconical flask,add 5.0mLof Internal standard solution,and mix.

Chromatographic system (see Chromatography á621ñ)— 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 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.8for phenylephrine hydrochloride and 1.0for 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 50µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in mg per mL,of USP Methylphenidate Hydrochloride RSin the standard stock solution used to prepare the Standard preparation;and RUand RSare the peak response ratios of the analyte to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.