Measurement of plasma angiotensin II: purification by cation-exchange chromatography.

Measurement of plasma angiotensin II (AII) by radioimmunoassay (RIA) usually requires prior purification of the plasma to remove substances that cross-react in the RIA, most notably angiotensin III (AIII). Purification of AII is generally accomplished by solid-phase extraction (SPE) followed by reverse-phase HPLC, with tedious evaporation and resuspension steps in between, and requires collection of many HPLC fractions per sample for RIA. In this report, we describe a rapid two-step SPE procedure for the purification of plasma AII, including an improved protease inhibitor cocktail for preventing the formation or degradation of AII in vitro.