Abstract: A high performance liquid chromatographic method to determine angiotensin-converting enzyme inhibitor activity in vitro was established by using N-hippuryl-His-Leu tetrahydrate as the reaction substrate and hippuric acid as the reaction product. The chromatographic conditions were as follows: column, ZORBAX SB-C18 (4.6 mm i.d.×150 mm, 5 μm); column temperature, 25 ℃; mobile phase, acetonitrile-distilled water (25∶75, v/v, both containing 0.05% (v/v) trifluoroacetic acid and 0.1% (v/v) triethylamine); flow rate, 0.5 mL/min; detection wavelength, 228 nm. An excellent linearity over the range of 0.005-1.000 mmol/L (r＝0.9999) was observed. The detection limit was 0.50 μmol/L. The recoveries of hippuric acid ware 99.48%-105.64%, with a relative standard deviation (RSD) of 2.20%(n＝6). It is a simple, precise and reliable assay method for developing antihypertension drugs.

Key words: angiotensin-converting enzyme inhibitor, hippuric acid , high performance liquid chromatography