A liquid chromatographic assay for urea in over-the-counter carbamide peroxide products

A liquid chromatographic assay has been developed and validated for determining the amount of urea present in carbamide peroxide formulations. The method employs an interaction CHO-620 carbohydrate column loaded in the Ca+2 form, a flow rate of 0.6 ml min-1, a column temperature of 85 degrees C, and UV detection at 200 nm. The mobile and stationary phase variables that may have an effect on the urea separation were studied and are discussed. The method was found to be linear over a range of 20 micrograms/g to 340 micrograms/g of urea, with a limit of detection of 1 microgram/g and a quantitation limit of 15 micrograms/g. System precision was found to have a %RSD of less than 1.0% while the method precision was typically less than 5.0%. Recoveries of 97.4% (1.0% RSD) and 98.3% (1.1% RSD) of the theoretical amount of urea (6.6% on a weight to weight basis) contained in two different formulations were obtained.