LC-MS Determination of Water for 3 Amphetamines with Enrichment by Dispersive SPE with Magnetic Carbon Nanotubes

Magnetic carbon nanotube material (Fe₃O₄@c-MWCNTs) was prepared by dissolving 4.70 g of FeCl₃·6H₂O and 1.72 g of FeCl₂·4H₂O in 280 mL of water at 80℃ and 2.00 g of carboxylated multi-walled carbon nanotubes (c-MWCNTs) were added together with 15 mL of aq. ammonia (28+72), under magnetic stirring and the stirring was continued for 30 min at 80℃. After standing, the solution was discarded and the black precipitate was washed thrice with water. The washings were discarded and the black precipitate was collected and dried in drying oven at 80℃ overnight. The magnetic material obtained was applied to the separation and enrichment of 3 amphetaminesi.e., methamphetamine (MA), 3,4-dimethoxyamphetamine (MDA) and methylcarcinone (MCN) from water sample. 5.0 mL of water sample were taken with its acidity adjusted to pH 12 with 1.0 mol·L^-1 NaOH solution (0.1 mL). 10.0 mg of Fe₃O₄@c-MWCNTs were added and the mixture was stirred ultrasonically for 1 min at 80 kHz, settled for 2 min, and Fe₃O₄@c-MWCNTs adsorbed with the amphetamines was to be pulled to a magnet placed at the outside wall of the glass vessel. The water solution was discarded and Fe₃O₄@c-MWCNTs was washed once more with 2 mL of water. After discarding the washing, the analytes on Fe₃O₄@c-MWCNTs were eluted ultrasonically twice with methanol (0.3 mL for each elution) at 80 kHz for 1 min in each elution. The eluates were combined and evaporated to near dryness by N₂-blowing. The residue was dissolved in 0.1 mL of methanol. The solution, after filtering through a membrane, was used for LC-MS analysis. Hypurity C₁₈ chromatographic column was used as the stationary phase and a mixture of methanol and 5 mmol·L^-1 acetic acid-ammonium acetate buffer solution (pH 4.0), in the volumic ratio of 80 to 20 was used as mobile phase in equivalent elution. ESI and SRM were adopted in MS. Linearity ranges for the 3 amphetamines were found same between 0.2-40.0 μg·L^-1, with detection limits (3S/N) of 0.015, 0.018, 0.020 μg·L^-1 respectively. Values of RSDs (n=5) found were in the range of 4.0% to 5.8%.