Determination of a process intermediate of celiprolol and its potential impurities by gradient high-performance...

3-(3-acetyl-4-hydroxyphenyl)-1,1-diethylurea (A-1354), is a synthetic intermediate of the beta-adrenergic blocker, celiprolol hydrochloride. A liquid chromatographic method has been developed and validated for the determination of bulk A-1354 and its potential impurities. High-low chromatography was used to improve the detectability of trace impurities. Enhanced chemical detectability was achieved by comparing the detector response of trace-impurity peaks from a stock sample solution (high-concentration) with the detector response for the A-1354 peak in a quantitatively diluted working sample solution (low-concentration). Chromatographic separation was achieved by gradient elution of A-1354 and its known impurities using an Ultrasphere C18 analytical column (5 microns, 250 x 4.6 mm i.d.). The gradient mobile phase components were methanol and 0.1% triethylammonium phosphate, pH = 4.0. The flow rate was 0.9 ml min-1 with UV absorbance detection at 236 nm. The method was determined to be specific, linear, precise and accurate for A-1354 and its known impurities. Known impurities of A-1354 are quantitated to 0.05% (w/w).