Investigation of degradation and penetration behaviors of dimethoate on and in spinach leaves using in situ SERS and LC-MS

• An in situ SERS method to detect dimethoate on and in spinach was established.
• SERS and LC-MS combined can track degradation behavior of dimethoate.
• Most pesticide molecules persisted on the surface of spinach for 21 days.
• Residues were mainly at 60–110 μm deep, in the palisade mesophyll layer of spinach leaves.

To investigate the degradation and penetration behaviors of the organophosphate insecticide dimethoate applied on spinach leaves, in situ SERS and LC-MS methods were used to detect dimethoate residue on&in spinach leaves picked on different days after treatment (DAT). The SERS and LC-MS methods determined that the dimethoate degradation rate followed first-order kinetics, with a half-life of 3.56 or 4.13 days, depending on the respective method. The correlation coefficient of quantification value of these two methods was 0.9562. With the SERS method, we detected most of the penetrated dimethoate in the depth of 60–110 μm. With the LC-MS method, we detected dimethoate up to 0.17 ng in leaves and that the dimethoate on:in ratio of spinach leaves ranged from 562.25 on 0 DAT to 5.23 on 14 DAT. The combination of these two methods facilitated a better understanding of the behavior and biological fate of pesticides in a complex biological system.

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