Developing solvent— Shake equal volumes of isobutyl alcohol and water in a separator, and allow the layers to separate. Use the upper layer as the Mobile phase and the lower layer as the Stationary phase.

p-Dimethylaminobenzaldehyde solution, 1%— Dissolve 1.0 g of p-dimethylaminobenzaldehyde in 50 mL of alcohol, add 2 mL of hydrochloric acid, and dilute with alcohol to 100.0 mL.

pH 6.5 Buffer solution— Mix 700 mL of 0.2 M dibasic sodium phosphate and 300 mL of 0.1 M citric acid.

Standard preparation— Prepare a solution of urea in water, containing 0.1 mg per mL.

Test preparation— Dissolve 10.0 mg of Hydroxyurea in 1.0 mL of water.

Procedure— Treat a suitable chromatographic paper strip (Whatman No. 1 or equivalent) by dipping it in pH 6.5 Buffer solution. Dry the paper strip, and apply 100 µL of the Test preparation and 50 µL of the Standard preparation. Place the strip in a chromatographic chamber for descending chromatography containing the Stationary phase in the bottom of the chamber and the Mobile phase in the trough. Develop for 24 hours, remove the strip from the chamber, air-dry, and develop again for 24 hours. Remove the strip, air-dry, spray with p-Dimethylaminobenzaldehyde solution, 1%, and heat at 90 for 1 to 2 minutes. Not more than two spots, other than the major component, are present in the Test preparation, and their intensities are not greater than the intensity of the spot from the Standard preparation (0.5% of each impurity). The Rr values relative to hydroxyurea, the principal spot, are 0.65 and 1.26 (urea).

(Official January 1, 2007)

Solution A— Dissolve 1.7 g of tetrabutylammonium hydrogen sulfate and 1.74 g of dibasic potassium phosphate, anhydrous, in 1000 mL of water, and adjust with 1 N sodium hydroxide or 85% phosphoric acid to a pH of 5.0.

Solution B: methanol.

Mobile phase— Prepare a solution of filtered, degassed Solution A and Solution B (8.5:1.5). Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Dissolve accurately weighed quantities of USP Hydroxyurea RS and hydroxylamine hydrochloride in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.4 mg per mL of each.

Standard preparation— Dissolve an accurately weighed quantity of USP Hydroxyurea RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.4 mg per mL.

Assay preparation— Transfer about 200 mg of Hydroxyurea, accurately weighed, to a 500-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 214-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 0.5 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between the hydroxylamine and hydroxyurea peaks is not less than 1.5; for the hydroxyurea peak, the column efficiency is not less than 5000; and the tailing factor 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 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 CH4N2O2 in the portion of Hydroxyurea taken by the formula: in which C is the concentration, in mg per mL, of USP Hydroxyurea RS in the Standard preparation; and rU and rS are the peak responses of the hydroxyurea peaks obtained from the Assay preparation and the Standard preparation, respectively.