Solidification of a Switchable Solvent-Based QuEChERS Method for Detection of 16 Pesticides in Some Fruits and Vegetables.

n-Octadecylamine was adopted as a cleanup agent to develop a novel solidification of a switchable solvent-based QuEChERS method. At higher temperatures (such as 55 °C), n-octadecylamine can melt into a liquid, allowing effective extraction of matrix interferences in acetonitrile solution (i.e., in dispersive liquid-liquid microextraction). At lower temperatures, n-octadecylamine carrying matrix interferences can rapidly solidify and easily separate from the acetonitrile solution. The results demonstrated that n-octadecylamine possessed a better ability to remove matrix interferences and reduce matrix effects than those of traditional solid-phase dispersive extraction cleanup agents of primary secondary amine and octadecyl bonded silica gel. By coupling it with gas chromatography-mass spectrometry, the proposed method was applied to the detection of 16 pesticides in cucumber. The recoveries were from 80.9 to 112.6% with relative standard deviations less than 12.9%. Satisfactory results were also obtained for the detection of 16 pesticides in pear, orange, apple, pepper, lettuce, and tomato.