In-sample derivatization-solid-phase microextraction of amphetamines and ecstasy related stimulants from water and urine

Abstract

A solid-phase microextraction (SPME) method for the determination of five amphetamine type stimulants (ATSs) in water and urine samples is presented. Analytes were simultaneously derivatized with iso-butyl chloroformate (iBCF) in the aqueous sample while being extracted, improving in this way the extractability of ATSs and permitting their determination by gas chromatography-mass spectrometry (GC-MS). The SPME procedure was carefully optimized in order to achieve adequate limits of detection (LODs) for environmental concentrations. Hence, different operational parameters were considered: type of SPME coating, ionic strength, basic catalyzer and derivatizing agent amount, extraction time and temperature. The final SPME procedure consists into the extraction of 100mL of sample containing 2 g of dipotassium monohydrogen phosphate trihydrate and 100 μL of iBCF (1:1 in acetonitrile), for 40 min at 60°C with a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber. Under these conditions, LODs in wastewater ranged from 0.4 to 2 ng L(-1), relative recoveries in the 84-114% range and relative standard deviations (RSD) lower than 15% were obtained. The application of the method to wastewater and river water samples showed the ecstasy ATS, 3,4-methylenedioxymethamphetamine (MDMA), as the most frequently detected, followed by methamphetamine, in concentrations around 20 ng L(-1). Finally, the method was downscaled and also validated with urine samples, proving its good performance with this matrix too: RSD<11%, recoveries in the 98-110% range and LODs lower than 0.1 μg L(-1).