## 1 Introduction
Therefore, some selective sorbents and methods should be developed for ensuring high analyte recoveries, good sensitivity, and low levels of co-extracted matrix compounds. Three-dimensional (3D) nanomaterials, with ultrahigh specific area, micropores, faster mass and electronic transport kinetics, and functional properties, provide great potentials for solving the above-mentioned problems. The 3D architectures with controlled micro- and nanostructure have been mainly used in supercapacitors, gas storage, sensors, batteries, and catalysis [18]. Hitherto, the studies on fabricating of 3D graphene-based composites and their application as sorbents have rarely been reported [19]. Within the past few years, much effort has been paid to the development of strategies for fabricating 3D-G architectures and compositions of graphene with other materials, e.g., carbon nanotubes, polymers, and metal oxides [20, 21]. A simple method for fabrication of a 3D microporous reduced graphene oxide (rGO)/polypyrrole nanotube (PNT)/magnetite (Fe\({}_{3}\)O\({}_{4}\)) hydrogel (3D-rGOPFH) nanohybrid is the self-assembly of graphene oxide (GO), PNT, and Fe\({}_{3}\)O\({}_{4}\) nanoparticles in a one-step hydrothermal reduction [22]. PNT was employed as a spacer between graphene sheets to avoid the stacking or aggregation of graphene sheets during the chemical reduction process, and a 3D porous structure of hydrogel with the high specific area was obtained. Polypyrrole is an advanced material of conducting polymer that is cheap, stable, and has good mechanical strength. Polypyrrole contains abundant-NH functional groups, large \(\pi\)-conjugated, and linear carbon chain structure, which is promising in separation science owing to its versatile properties such as hydrogen bonding, ion exchange property, electroactivity, hydrophobicity, large \(\pi\)-conjugated structure, and so on [23]. On the basis of these versatile properties, PNT is expected to improve the adsorption ability of graphene for different classes of insecticides. Additionally, a previous study showed that appropriate pores of nanomaterials could exclude large compounds but allow small compounds to enter, resulting in the separation of compounds with different molecular sizes [24]. The interference compounds in the extract of vegetable matrices are usually long alkyl chains-containing phenols, esters, acids, and alcohols [25]. These large molecules are usually in oligomers larger than 10 nm [26], while the molecular size of a pesticide is relatively small (sub-nanometer level) [27; 28]. So, the pesticides can be separated from the vegetable matrices by porous material with a proper pore size, which will minimize the reduction of the matrix effects. The 3D-rGOPFH combines the virtue of 3D architecture of rGO, PNT, and Fe\({}_{3}\)O\({}_{4}\) nanoparticles, which makes it a promising sorbent for different compounds in sample preparation techniques. In this study, the 3D-rGOPFH nanocomposite was synthesized according to the recently reported method [22] and its potential application for the enrichment of insecticide residues in vegetables was studied. Thirteen insecticides, including widely applied OPPs, OCPs, pyrethroids, triazoles, and carbamates, were selected as representative targets, and gas chromatography-tandem mass spectrometry (GC-MS/MS) was performed for the study. The results demonstrated that this is a simple, sensitive, and effective MSPE method for the detection of multi-insecticide residues in vegetables.