Determination of twelve herbicides in tobacco by a combination of solid–liquid–solid dispersive extraction using multi-walled carbon nanotubes, dispersive liquid-liquid micro-extraction, and detection by GC with triple quadrupole mass spectrometry

We report on a method for the determination of twelve herbicides using solid–liquid–solid dispersive extraction (SLSDE), followed by dispersive liquid-liquid micro-extraction (DLLME) and quantitation by gas chromatography with triple quadrupole mass spectrometric detection. SLSDE was applied to the extraction of herbicides from tobacco samples using multi-walled carbon nanotubes (MWCNTs) as clean-up adsorbents. The effect of the quantity of MWCNTs on SLSDE, and of type and volume of extraction and disperser solvents and of salt effect on DLLME were optimized. Good linearity is obtained in the 5.0 - 500 μg kg −1 concentration range, with regression coefficients of >0.99. Intra-day and inter-day repeatability, expressed as relative standard deviations, are between 3 and 9 %. The recoveries in case of herbicide-spiked tobacco at concentration levels of 20.0, 50.0 and 100.0 g kg −1 ranged from 79 to 105 %, and LODs are between 1.5 and 6.1 μg kg −1 . All the tobacco samples were found to contain butralin and pendimethalin at levels ranging from 15.8 to 500.0 μg kg −1 . Figure Schematic diagram of herbicide extraction from tobacco samples by SLSDE-DLLME procedures. (a) sample solution containing herbicide and 10 mL acetonitril, (b) MWCNTs cleanup, (c) extract mixed with water, (d) addition of 100 μL of extraction solvent(chloroform) into mixed solution, (e) vortex mixer for 1 min, (f) phase separation after centrifugation. ► A method for analysis of 12 herbicides in tobacco samples was developed. ► MCNTs were used as sorbent, DLLME was further applied to purification and enrichment.. ► Butralin and pendimethalin were found in all tobacco samples.