Single drop liquid–liquid–liquid microextraction of methamphetamine and amphetamine in urine

Single drop liquid–liquid–liquid microextraction (LLLME) combined with high performance liquid chromatography (HPLC)–UV detection was investigated for the determination of a popular drug of abuse, methamphetamine (MAP), and its major metabolite, amphetamine (AP), in urine samples. The target compounds were extracted from NaOH modified sample solution to a thin layer of organic solvent membrane, and back-extracted to an acidic acceptor drop suspended on the tip of a 50-μL HPLC syringe in the aforementioned organic layer. This syringe was also used for direct injection after extraction. Factors affecting extraction efficiency were studied. At optimal conditions, the overall enrichment factor (EF) was 500-fold for AP and 730-fold for MAP, respectively. The method exhibited a wide linear range (1.0–1500 μg/L), low detection limit (0.5 μg/L), and good repeatability (RSD < 5.0%) for both analytes. The feasibility of the method was demonstrated by the analysis of human urine samples.