Determination of amphetamine-type stimulants in urine samples using microextraction by packed sorbent and gas chromatography-mass spectrometry.

The aim of this work was the development, optimization and full validation of a method applying microextraction by packed sorbent (MEPS) coupled to gas chromatography-mass spectrometry (GC-MS) to determine amphetamine (AMP), methamphetamine (MAMP), 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxyethylmethamphetamine (MDMA), 3,4-methylenedioxy-N-methyl-α-ethylfenilethylamine (MBDB), and 3,4-methylenedioxy-N-ethylamphetamine (MDE) in urine samples. Using 200 µL of sample, the MEPS procedure was optimized concerning type of sorbent, sample dilution, number of strokes, activation of the ion exchange mechanism and composition of both washing and elution solvents. The method was fully validated according to the Food and Drug Administration and the Scientific Working Group of Forensic Toxicology guidelines for the validation of bioanalytical methods. The studied parameters included selectivity, calibration model and linearity, limits of detection and quantification, precision, accuracy, stability, dilution integrity and recoveries. Linearity was obtained in the range of 25-1000 ng/mL for MAMP, MBDB and MDE, 35-1000 ng/mL for AMP and MDMA, and 50-1000 ng/mL for MDA, with coefficients of determination (R2) >0.99 for all analytes. Both intra- and inter-day precision and accuracy were adequate, and coefficients of variation lower than 15% and mean relative errors (RE) within a range of ±15% of the theoretical concentrations were obtained for all compounds under study. Analyte recoveries ranged from 19 to 71%, allowing LLOQs ≤50 ng/mL.