Sensitive magnetic solid-phase microextraction based on oxide multi-walled carbon-nanotubes for the determination of methylamphetamine and ketamine in human urine and blood

Abstract

A sensitive and rapid magnetic solid-phase microextraction (MSPE) procedure based on multi-walled carbon nanotubes (MWNTs), combined with gas chromatography-mass spectrometry (GC-MS), was developed for the quantification of two illegal basic drugs, methamphetamine (MA) and ketamine (KT), in human urine and whole-blood samples. Acid-oxidized MWNTs (o-MWNTs), selected as the adsorbent, have good affinity to these two drugs due to the π–π stacking interactions derived from the aromatic rings, and to the hydrogen bonds provided by the chelation sites of oxygen-containing functional groups on their surfaces. Ionic strength, pH level, desorption solvent and extraction time were optimized in sequence to yield the highest signal response for the two drugs. Under optimized conditions, the calibration curves were linear over the range of 0.2–50 ng mL⁻¹ with R² higher than 0.99, and resulted in good precision (6.8–7.1% for intra-day, 7.4–9.2% for inter-day). The limits of detection for MA and KT were 0.044 and 0.024 ng mL⁻¹, respectively, which were below the cut-off values recommended by the United Nations Office on Drugs and Crime (UNODC), and were lower than those of other reported analytical methods. The application feasibility of the method in illegal drug monitoring was demonstrated by analyzing the urine and blood samples collected from a nonuser volunteer and a suspected drug abuser in a forensic case, respectively. Solvent extraction for protein precipitation before the MSPE procedure involved here was confirmed to improve the recoveries in dealing with biological samples. This method is simple, sensitive, and provides an accurate and sensitive detection platform for drug abuse analysis.