Reagent A— Dissolve 8.5 g of tetrabutylammonium hydrogen sulfate in 80 mL of water. Add 3.4 mL of phosphoric acid, and adjust with 10 N sodium hydroxide to a pH of 7.55.

Mobile phase— Add 20 mL of Reagent A to a mixture of 880 mL of water and 100 mL of acetonitrile, mix, filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of 1,1-cyclobutanedicarboxylic acid in Mobile phase to obtain a solution having a known concentration of about 0.5 mg per mL. Transfer 2.0 mL of this solution to a 200-mL volumetric flask, dilute with Mobile phase to volume, and mix.

System suitability solution— Mix 1.0 mL of the Standard solution with 1.0 mL of Standard preparation, prepared as directed in the Assay.

Test solution— Transfer about 50 mg of Carboplatin, accurately weighed, to a 50-mL volumetric flask. Dissolve in and dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 220-nm detector and a 4.0-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph replicate injections (about 100 µL) of the System suitability solution, record the chromatograms, and measure the peak responses: the relative retention times are about 0.65 for carboplatin and 1.0 for 1,1-cyclobutanedicarboxylic acid; the column efficiency, determined from the 1,1-cyclobutanedicarboxylic acid peak, is not less than 1500 theoretical plates; the resolution, R, between carboplatin and 1,1-cyclobutanedicarboxylic acid peaks is not less than 2.5; and the relative standard deviation for replicate injections is not more than 10%.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses for the 1,1-cyclobutanedicarboxylic acid peaks. Calculate the percentage of 1,1-cyclobutanedicarboxylic acid in the portion of Carboplatin taken by the formula: in which C is the concentration, in µg per mL, of 1,1-cyclobutanedicarboxylic acid in the Standard solution, W is the weight, in mg, of Carboplatin taken to prepare the Test solution, and rU and rS are the peak responses for 1,1-cyclobutanedicarboxylic acid obtained from the Test solution and the Standard solution, respectively: not more than 0.5% is found.

Mobile phase, Chromatographic system, and Procedure— Proceed as directed in the Assay.

Standard solution— Quantitatively dilute a volume of the Standard preparation, prepared as directed in the Assay, with water to obtain a solution having a known concentration of about 2.5 µg of USP Carboplatin RS per mL.

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. The sum of the peak responses, excluding the carboplatin and 1,1-cyclobutanedicarboxylic acid responses, from the Test solution, is not more than 2 times the carboplatin response from the Standard solution, and no single peak response is greater than that of the carboplatin peak from the Standard solution: not more than 0.25% of any individual impurity is found, and the sum of all impurities is not more than 0.5%.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (87:13). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Carboplatin RS in water, and quantitatively dilute with water to obtain a solution having a known concentration of about 1 mg per mL. [note—Use this solution within 2 hours.]

Assay preparation— Transfer about 50 mg of Carboplatin, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with water to volume, and mix. [note—Use this solution within 2 hours.]

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 230-nm detector and a 4.0-mm × 30-cm column that contains packing L8. The flow rate is about 2.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the capacity factor, k¢, is not less than 3.0, the column efficiency is not less than 2500 theoretical plates, the tailing factor is not more than 2.5, and the relative standard deviation for replicate injections is not more than 1.2%.

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 major peaks. Calculate the quantity, in mg, of C6H12N2O4Pt in the portion of Carboplatin taken by the formula: in which C is the concentration, in mg per mL, of USP Carboplatin RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.