Determination of free (unconjugated) amphetamine-type stimulants in urine samples by dispersive liquid–liquid microextraction and gas chromatography coupled to mass spectrometry (DLLME-GC-MS)

Abstract The consumption of drugs of abuse is a growing practice in the modern world. Synthetic drugs and amphetamine derivatives in particular occupy a prominent place. The consumption of stimulants such as amphetamine-type fenproporex (FEN), diethylpropione (DIE) and sibutramine (SIB) has become a common practice among professional drivers in Brazilian highways in recent years and among people who wish to lose weight, but make use of these substances indiscriminately. The present work is the development of an analytical method using dispersive liquid–liquid microextraction (DLLME), able to extract and preconcentrate these medicines, in their unchanged form, at low concentrations in urine samples. The analyses were performed using gas chromatography coupled to mass spectrometry (GC-MS). The method presented good analytical performance, with excellent linearity in the dynamic range of 1 to 1000 ng mL − 1 for DIE, FEN and SIB, with values of R 2 equal to 0.9926, 0.9994 and 0.9951, respectively. The limits of detection (LOD) were of 0.1 ng mL − 1 for DIE and FEN and 0.05 ng mL − 1 for SIB. The intraday precision ranged between 6.6% and 7.9% while the interday ranged between 3.9% and 5.5%. The relative recoveries obtained were, in average, 92.9% for DIE, 96.6% for FEN and 91.7% for SIB. Twenty urine samples, obtained from the Forensic Toxicology Laboratory, were then analyzed for the presence of DIE, FEN and SIB, using the analytical method developed in this work. None of the analytes were found in these samples, probably due to a decrease in their consumption, mainly because of the prohibition in the manufacturing and marketing of DIE and FEN, together with a more rigorous control in the sales of SIB in Brazil. This also confirmed the preliminary results from a screening conducted by immunoassay techniques. Therefore, the method developed proved to be quite useful in the analysis of the studied compounds in urine samples, post mortem or in vivo .