Micro-method for the determination of piperacillin in plasma by high-performance liquid chromatography

A simple and sensitive high-performance liquid chromatographic method for the determination of piperacillin in plasma is described. A C8 reversed-phase column was used with a mobile phase consisting of methanol-water-triethylamine (550:450:4, v/v/v) adjusted to pH = 3 with orthophosphoric acid and UV detection at 270 nm. Cephalothin was used as internal standard. The method involves a plasma protein precipitation with acetonitrile followed by extraction of endogenous compound with chloroform and injection of the upper aqueous phase into the chromatograph. Within-day and between-day assays give relative standard deviations less than or equal to 5.7%. The detection limit is 0.2 microgram ml-1. Stability studies show that piperacillin degradation starts at -4 degrees C. Therefore, samples have to be processed promptly and stored at -20 degrees C. The method described is convenient for clinical monitoring and for pharmacokinetic studies.