Development of a liquid chromatography–tandem mass spectrometric method for the determination of methamphetamine and amphetamine using small volumes of rat serum

The aim of this paper was to develop LC/MS/MS methodology for the determination of methamphetamine (METH) and amphetamine (AMP) using low microliter volumes (20–150 μl) of rat serum and demonstrate the use of this method for the study of serum pharmacokinetics in the rat. The analytes were extracted from rat serum using solid-phase extraction followed by an isocratic separation on a narrow-bore Hypersil C18 column. Lower limits of quantitation for METH and AMP were 0.3 ng/ml using positive ion electrospray tandem mass spectrometry. The accuracy of the method was within 20% of the actual values over a wide range of serum concentrations. The within-day and between-day precision was better than 20% (R.S.D.). Ion-suppression matrix effects on electrospray ionization were evaluated for extracted rat serum. The LC/MS/MS method was further validated by comparing serum concentrations of METH and AMP to serum concentrations previously determined using an LC/[3H]-METH assay with radiochemical detection. Finally, the LC/MS/MS method was used to study the pharmacokinetics of METH and AMP after a 1 mg/kg intravenous bolus dose of METH to female Sprague–Dawley rats.