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

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, 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 approximately 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.