A novel, simple, and rapid method for determination of the residues of 44 commonly used pesticides in tobacco was developed based on modified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) procedures. The pesticides were extracted with acetonitrile and purified on a mixed sorbents column of primary secondary amine, C18, and graphitized carbon black. Quantitative determination of all pesticides was performed by ultra-performance LC/MS/MS in the positive or negative ionization mode by a single run due to the fast polarity switching capability of the mass spectrometer. Two precursor-product ion transitions were monitored for each compound in the multiple reaction monitoring mode. Quantification was carried out using matrix-matched standard calibration. The method has been validated by various tobacco cultivars, such as Burley, Oriental, and Virginia from different countries. Recoveries of the proposed method for spiked samples ranged from 71.1 to 109.8%, and RSD values were below 10%. The LOQ values were are all below the guidance residue levels proposed by the Agrochemical Advisory Committee of Cooperation Center for Scientific Research Relative to Tobacco. This method is valuable for measurement of pesticide residues in tobacco for QC and monitoring.

No abstract

A method has been developed for the quantitation of imazaquin residues in soil. The herbicide was extracted from soil with methanolwater (2 + 1, v/v) and cleaned up by strong anion-exchange solid-phase extraction cartridges. Analysis was performed by using high-performance liquid chromatography with ultraviolet detection. Average recoveries through the method ranged from 90.7 to 100.6%, with relative standard deviation equal to or lower than 6.6%. The limit of detection was estimated to be 0.0015 mg/kg, and the minimum quantitation concentration of imazaquin in soil was 0.005 mg/kg. This method was successfully applied to evaluate imazaquin residue levels in soil and its dissipation rates in a soybean field in the Xisanqi District of Beijing, People's Republic of China. The dissipation study showed that the half life of imazaquin in soil was 10.37 0.0135 days at 3 different application rates.