Simultaneous determination of amoxicillin and clavulanic acid in human plasma by HPLC–ESI mass spectrometry

A simple, fast and sensitive high-performance liquid chromatography (HPLC)–mass spectrometric (MS) method has been developed for simultaneous determination of amoxicillin and clavulanic acid in human plasma using terbutaline as internal standard. After precipitation of the plasma proteins with acetonitrile, the analytes were separated on a C8 reversed-phase column with formic acid–water–acetonirile (2:1000:100) and detected using electrospray ionization (ESI) mass spectrometry in negative selected ion monitoring (SIM) mode. The method was validated and successfully applied to analysis of amoxicillin and clavulanic acid in clinical studies. The limit of quantitation, 0.12 μg/ml for amoxicillin and 0.062 μg/ml for clavulanic acid, was five times lower than that of the published HPLC–UV method.