Screening procedure for 21 amphetamine-related compounds in urine using solid-phase microextraction and gas chromatography-mass spectrometry.
A specific, sensitive, and rapid procedure for the screening of 21 amphetamine-related compounds in urine is developed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry. Very clean extracts are obtained in one step with SPME using silica fibers coated with a 100-micron polydimethylsiloxane stationary phase. Temperature, time, pH, and salt saturation are optimized to obtain consistent extraction. An excellent chromatographic separation of the underivatized analytes is obtained with a specially treated nonpolar capillary column (Supelco PTA-5, 30 m x 0.32-mm i.d., 0.5-micron film thickness) dedicated to amino compounds. Selected ion monitoring of three fragments per analyte and one for each of the three deuterated internal standards elicits a high selectivity and detection limits between 1 and 50 ng/mL (i.e., low enough to verify positive results obtained with immunochemical assays). The method is linear in a narrow range (from the detection limit up to 500 ng/mL) when all the amphetamines are assayed together but shows a good linearity up to 2000 ng/mL when the molecules are determined individually. Repeatability is not satisfactory for all compounds but could probably be improved by strictly controlling the extraction time (e.g., by automating the whole procedure using an autosampler). The use of SPME reduces the interference due to urinary low-volatility organic compounds and avoids the risks related to the use of organic solvents. To our knowledge, this technique is the first one allowing the sensitive determination of such a number of amphetamine analogs.