Medium: 0.1 N hydrochloric acid; 500 mL, deaerated.

Apparatus 2: 50 rpm.

Time: 10 minutes.

Standard solution— Accurately weigh an amount of USP Ondansetron RS, and dilute with Medium to obtain a solution having a final concentration of 0.01 mg per mL for Tablets labeled to contain 4 mg, and a final concentration of 0.02 mg per mL for Tablets labeled to contain 8 mg.

Test solution— Pass a portion of the solution under test through a filter.

Procedure— Determine the amount of C18H19N3O dissolved by UV absorption at the wavelength of maximum absorbance at about 310 nm on portions of the Test solution in comparison with the Standard solution, using a 1-cm cell. Calculate the amount, in percentage, of ondansetron released by the formula: in which AU and AS are the absorbances obtained from the Test solution and the Standard solution, respectively; WS is the weight, in mg, of USP Ondansetron RS taken; 500 is the volume, in mL, of Medium; 100 is the conversion factor to percentage; D is the dilution factor of the Standard solution; and L is the Tablet label claim, in mg.

Tolerances— Not less than 80% (Q) of the labeled amount of C18H19N3O is dissolved in 10 minutes.

Phosphate buffer— Prepare as directed in the Assay.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate buffer and acetonitrile (8:2). Make adjustments if necessary (see System Suitability under Chromatography 621).

Ondansetron related compound D solution— Dissolve an amount of USP Ondansetron Related Compound D RS in acetonitrile, and dilute stepwise with Mobile phase to obtain a solution having a known concentration of about 0.04 mg per mL.

2-Methylimidazole solution— Dissolve an amount of 2-methylimidazole in acetonitrile, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.04 mg per mL.

Standard stock solution— Dissolve an accurately weighed quantity of USP Ondansetron RS in acetonitrile, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.04 mg per mL.

System suitability solution— Transfer 5.0 mL each of Standard stock solution, 2-Methylimidazole solution, and Ondansetron related compound D solution to a 100-mL volumetric flask. Dilute with Mobile phase to volume, and mix.

Standard solution— Pipet 5.0 mL of the Standard stock solution into a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

System sensitivity solution— Pipet 10.0 mL of the Standard solution into a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Test solution— Transfer 10 Tablets to an appropriate volumetric flask so that the final concentration of ondansetron is about 400 µg per mL. Add Mobile phase to fill about 60% of the flask capacity. Shake by mechanical means for about 5 minutes, and dilute with Mobile phase to volume. Centrifuge a portion of this solution at 3000 rpm for 10 minutes. Use the supernatant.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 216-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 System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are given in Table 1; the resolution, R, between ondansetron and any adjacent peak is not less than 1.5; the column efficiency is not less than 8000 theoretical plates for ondansetron; and the tailing factor for the ondansetron peak is not more than 2.0. Chromatograph the System sensitivity solution, and record the peak responses as directed for Procedure: the signal-to-noise ratio for the ondansetron peak is not less than 15. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Inject a volume (about 20 µL) of the Test solution and the Standard solution into the chromatograph, record the chromatograms, and measure the peak responses. 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 Ondansetron RS in the Standard solution; F is the relative response factor for each impurity as specified in Table 1; V is the volume, in mL, of the volumetric flask used to prepare the Test solution; D is the amount, in mg, of ondansetron in the sample based on the labeled amount and number of Tablets taken; ri is the peak area of any impurity in the Test solution; and rS is the peak area of ondansetron in the Standard solution: it meets the requirements specified in Table 1. [note—The run time is about 60 minutes.]

Diluent: 0.01 N hydrochloric acid.

Phosphate buffer— Dissolve about 2.72 g of monobasic potassium phosphate in 1000 mL of water. Adjust with 1 N sodium hydroxide or 0.5 N sodium hydroxide to a pH of 5.4.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate buffer and acetonitrile (52:48). Make adjustments if necessary (see System Suitability under Chromatography 621).

Ondansetron related compound A solution— Dissolve an amount of USP Ondansetron Related Compound A RS in Diluent, and dilute stepwise with Diluent to obtain a solution having a known concentration of about 0.14 mg per mL.

Concentrated assay preparation— Transfer 10 Tablets to an appropriate volumetric flask so that the final concentration is about 400 µg of ondansetron per mL. Add Diluent to fill about 60% of the flask capacity. Shake by mechanical means for about 5 minutes, and dilute with Diluent to volume. Filter a portion of this solution through a 0.45-µm polypropylene membrane, discarding the first 5 mL of the filtrate.

System suitability solution— Transfer 8.0 mL of Ondansetron related compound A solution and 8.0 mL of the Standard preparation to a 50-mL volumetric flask. Dilute with Diluent to volume, and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Ondansetron RS in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 40 µg per mL.

Assay preparation— Transfer 5.0 mL of the Concentrated assay preparation to a 50-mL volumetric flask. Dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 216-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 System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 1.1 for ondansetron related compound A, and 1.0 for ondansetron; the resolution, R, between ondansetron related compound A and ondansetron is not less than 1.5; and the tailing factor is not more than 2.0 for the ondansetron peak. 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the ondansetron peaks. Calculate the quantity, in mg, of ondansetron (C18H19N3O) in the portion of Tablets taken by the formula: in which V is the volume used to prepare the Concentrated assay preparation; C is the concentration, in mg per mL, of USP Ondansetron RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.