Sample preparation

The QuEChERS procedure is the combination of an extraction step for pesticides in fruits and vegetables and a cleanup step that removes sugars, lipids, and organic acids. And some modifications to the original QuEChERS method have been introduced to ensure efficient extraction of pH-dependent compounds in the vegetables and fruits. Initially, each chopped and homogenized sample (20.0 g) was placed in a 50 mL centrifuge tube, then a mixture of 20.0 mL of acetonitrile:toluene (1:1, v/v, containing 0.25% HCl) was added, and the sample was vortexed for 3 min. Subsequently, 5.0 g of NaCl was added, the tubes were immediately vortexed intensively for 2 min, and then centrifuged at 5000 r min⁻¹ for 5 min. Next, 0.1 mL of the upper layer was transferred into a single-use centrifuge tube, diluted with 0.9 mL of methanol, and filtered through a 0.22 μm nylon syringe filter prior to UHPLC–MS/MS injection.