A: Infrared Absorption 197K.

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.

Buffer solution, Solution A, Solution B, Mobile phase, Diluent, System suitability solution, and Chromatographic system— Prepare as directed in the Assay.

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

Test solution— Use the Assay preparation.

Procedure— Inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, and record the chromatogram. Identify the impurities using the relative retention times given in Table 1, and measure the peak responses. Calculate the percentage of each risperidone related compound in the portion of Risperidone taken by the formula: in which CS and CU are the concentrations, in mg per mL, of risperidone in the Standard solution and the Test solution respectively; rU is the peak area of each impurity obtained from the Test solution; rS is the peak area of risperidone obtained from the Standard solution; and F is the relative response factor for each impurity relative to risperidone. In addition to not exceeding the limits in Table 1, not more than 0.10% of any unknown impurity (use F value of 1.0) is found and not more than 0.30% of the total impurities is found. Disregard the impurity peaks that are less than 0.05%.

Buffer solution— Dissolve 15.4 g of ammonium acetate in 1 L of water. Adjust with 10% acetic acid to a pH of 6.5, and mix.

Solution A— Mix 100 mL of Buffer solution with 150 mL of methanol in a 1000-mL volumetric flask, and dilute with water to volume.

Solution B— Mix 100 mL of Buffer solution with 850 mL of methanol in a 1000-mL volumetric flask, and dilute with water to volume.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluent— Mix 100 mL of Buffer solution with 900 mL of water and 1000 mL of methanol.

System suitability solution— Prepare a 1 mg per mL solution of USP Risperidone System Suitability Mixture RS in Diluent.

Standard preparation— Dissolve an accurately weighed quantity of USP Risperidone RS in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 1.0 mg per mL.

Assay preparation— Dissolve an accurately weighed quantity of Risperidone in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a concentration of about 1.0 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 275-nm detector and a 4.6-mm × 10-cm column that contains 3-µm packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 35. The chromatograph is programmed as follows. Inject the System suitability solution. Record the peak responses as directed for Procedure, and identify the peaks due to Z-oxime, 9-hydroxyrisperidone, 6-methylrisperidone, and risperidone using the relative retention times (RRT) from Table 1; the resolution, R, between Z-oxime and 9-hydroxyrisperidone is not less than 2.8; the tailing factor for risperidone is not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0% for the risperidone peak.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, and measure the responses for the risperidone peak. Calculate the quantity, in percent of C23H27FN4O2, in the portion of Risperidone taken by the formula: in which CS and CU are the concentrations, in mg per mL, of risperidone in the Standard preparation and the Assay preparation, respectively; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.