A: Infrared Absorption— Grind 10 Tablets to a fine powder. Transfer an amount of powder, equivalent to 3 mg of tolcapone, into a polystyrene vial containing two mixing beads. Add 300 mg of IR grade potassium bromide, and disperse the material in the matrix by agitating the capped vial in a grinding mill for 2 minutes. Transfer a portion of the sample to a sample cup. Record the diffuse reflectance IR spectrum between 2200 and 1090 cm–1 (see Spectrophotometry and Light-Scattering 851). The spectrum thus obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Tolcapone RS, concomitantly measured.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Medium: pH 6.8 phosphate buffer containing 1% of sodium lauryl sulfate; 900 mL.

Apparatus 2: 75 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C14H11NO5 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 271 nm on filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Tolcapone RS in the same Medium. Calculate the amount of C14H11NO5 dissolved in each Tablet.

Tolerances— Not less than 75% (Q) of the labeled amount of C14H11NO5 is dissolved in 30 minutes.

Diluent 1, Diluent 2, System suitability solution, Mobile phase, and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Use the Standard preparation, prepared as directed in the Assay.

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the areas for the major tolcapone peaks. Calculate the percentage of each impurity in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Tolcapone RS in the Standard solution; A is the average weight, in mg, of the Tablets; W is the weight, in mg, of tablet powder taken to prepare the Test solution; D is the labeled quantity, in mg, of tolcapone per Tablet; ri is the peak area for any impurity in the Test solution; and rS is the peak area for tolcapone in the Standard solution: not more than 0.1% of any individual impurity is found, and not more than 0.5% of total impurities is found.

Diluent 1— Prepare a mixture of methanol and acetonitrile (24:15).

Diluent 2— Prepare a mixture of methanol, water, and acetonitrile (8:7:5).

System suitability solution— Dissolve an accurately weighed quantity of USP Tolcapone RS, USP Tolcapone Related Compound A RS, and USP Tolcapone Related Compound B RS in Diluent 2, and dilute quantitatively, and stepwise if necessary, with Diluent 2 to obtain a solution having a known concentration of about 104 µg per mL, 10.4 µg per mL, and 10.4 µg per mL, respectively.

Mobile phase— Prepare a filtered and degassed mixture of methanol, 0.05 M monobasic potassium phosphate having a pH of 2.0 ± 0.1, and acetonitrile (8:7:5). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Tolcapone RS in Diluent 1, and dilute quantitatively, and stepwise if necessary, with Diluent 1 to obtain a solution having a known concentration of about 1.0 mg per mL. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, add about 27.5 mL of Diluent 1, dilute with water to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of tolcapone, to a 100-mL volumetric flask, add 10 mL of water, and sonicate for about 10 minutes. Add 65 mL of Diluent 1, and sonicate for about 15 minutes. Allow the sample to settle. If the material is still undispersed, sonicate for an additional 5 minutes. Dilute with water to volume, and mix. Centrifuge a portion of this solution, and transfer 5.0 mL of the supernatant to a 50-mL volumetric flask. Dilute with Diluent 2 to volume, and mix. Pass a portion of this solution through a 0.45-µm filter, and use the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector and a 4.0-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.6 for tolcapone related compound A, 1.0 for tolcapone, and about 1.4 for tolcapone related compound B; the resolution, R, between tolcapone related compound B and tolcapone is not less than 6.0; and the tailing factor for the tolcapone peak is not more than 1.5. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for 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 tolcapone (C14H11NO5) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Tolcapone RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.