## 4 Conclusions  
In this study, a 3D-rGOPFH nanohybrid was successfully fabricated by a self-assembly of rGO nanosheets decorated with PNT and Fe\({}_{3}\)O\({}_{4}\) nanoparticles. Then the nanohybrid was used as MSPE sorbent for simultaneous preconcentration of thirteen insecticides in vegetable samples followed by GC-MS/MS determination. PNT that functions as a spacer avoids the stacking or aggregation of graphene sheets and improves the affinity of material for analytes via providing multiple adsorption interactions, such as hydrogen bonding, electrostatic interaction, \(\pi\)-\(\pi\) stacking interaction, and hydrophobic interaction force. Compared to other reported Fe\({}_{3}\)O\({}_{4}\), 2D-G-Fe\({}_{3}\)O\({}_{4}\), PNT/Fe\({}_{3}\)O\({}_{4}\), and 3D-G-Fe\({}_{3}\)O\({}_{4}\) sorbents, 3D-rGOPFH exhibits better adsorption efficiency and analyte-compatibility for different classes of insecticides. Furthermore, 3D-rGOPFH effectively excludes the interfering compounds, and clean analytes were obtained by elution and analyzed using GC-MS/MS. The magnetic nanohybrids help convenient separation of sorbent from the sample solution by an external magnetic field without the need for centrifugation or filtration procedures. In all cases, a low limit of detections of 0.006-0.03 ng g\({}^{-1}\) and satisfactory recoveries of 79.2-109.4% were obtained with RSD \(\leq\)8.8%. These results indicated the developed method is a facile, environment-friendly, time and energy-saving, and sensitive sample preparation technique to determine multi-insecticide residues. The proposed method is expected to be widely applied for determining other organic pollutants in different samples in our further study. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/10/16/5665/s1](http://www.mdpi.com/2076-3417/10/16/5665/s1)]([http://www.mdpi.com/2076-3417/10/16/5665/s1](http://www.mdpi.com/2076-3417/10/16/5665/s1)), Figure S1: (a) XRD analysis of GO, rGO, PNT, Fe\({}_{3}\)O\({}_{4}\) nanoparticle, and 3D-rGOPFH. (b) VSM magnetization curve of 3D-rGOPFH., Figure S2: Effect of different loading amounts of PNT (m\({}_{\text{PNT}}\):m\({}_{\text{GO}}\) = 20:1, 16:1, 12:1, 8:1, 4:1, 2:1, 1:1, and 1:2) on extraction efficiency., Figure S3: Effect of (a) desorption solvent, (b) desorption time, (c) extraction time, (d) sorbent dosage, (e) pH, (f) ionic strength, (g) methanol content, and (h) desorption volume on extraction efficiency of MSPE by using 3D-rGOPFH. Table S1: Chemical structure, type, molecular weights, retention time, ion transition and Log p of the target compounds, Table S2: Matrix effect values of insecticides in tomato, cucumber, and pakchoi samples. **Author Contributions:** Conceptualization, S.W. and H.L. ; methodology, S.W. ; software, S.W. ; validation, S.W. and S.L. ; investigation, S.W. ; writing--original draft preparation, S.W., X.L. ([PERSON]), M.L., X.L. ([PERSON]), X.L. ([PERSON]), Q.Z., and H.L. ; writing--review and editing, S.W. and H.L. ; supervision, H.L. ; funding acquisition, S.W. and H.L. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Key R&D Program of China (2019 YFC1604800). **Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.