Simultaneous supercritical fluid extraction and chemical derivatization for the gas chromatographic–isotope dilution mass spectrometric determination of amphetamine and methamphetamine in urine

Abstract

An in-situ supercritical fluid extraction (SFE) and chemical derivatization (ChD) procedure followed by gas chromatography–isotope dilution mass spectrometry (GC–MS) for the determination of amphetamines in urine is described and evaluated. While using celite as the SFE wet-support, the one-pot sample pretreatment procedure also employs ammonium water to alkalize the urine matrix that contains protonated amphetamine (AP) and methamphetamine (MA). The mean recoveries achieved by simultaneous SFE–ChD, i.e., 95% (RSD=3.8%) for AP and 89% (RSD=4.0%) for MA, are significantly better than the corresponding overall recoveries obtained upon stepwise SFE–ChD, suggesting the unreacted trifluoroacetic anhydride (TFA) in the former procedure has strengthened the extracting power of CO 2 fluid as has been evidenced by a control test. As to GC–MS analysis, the optimal qualitative ions and quantitative ions of the respective analytes were determined via a rigorous evaluation process. Thus, the regression calibration curves for AP and MA in urine are linear within 100∼50 000 ng/ml, with correlation coefficients typically exceeding 0.999. The limits of detection determined by two methods for AP and MA vary from 19 to 50 ng/ml, and limits of quantitation from 21 to 100 ng/ml. Precisions calculated for the triplicate analyses of AP and MA in a 500-ng/ml spiked control, two real-case samples and two quasi real-case samples, respectively, using regression calibration are typically below 10%. The method is simple and reliable. It may serve as an alternative to the existing confirmatory protocol for forensic urine drug testing.