## 1 Introduction  
Fungicides are among the most extensively exploited pesticides to destroy or prevent the growth of many plant pathogenic fungi in modern agriculture. Generally, due to their curative, protective, and eradication functions, which are resistant to a large variety of crop fungal diseases [1; 2], carbendazim, thiophanate-methyl, pyrimethanil, metalaxyl, prochloraz, procymidone, dimethomorph, triadimefen, and difenoconazole are widely applied in the cultivation of fruit, vegetables, and other crops. However, commonly used fungicides are highly toxic, and many of them have been proved to enerate the liver function, change the urinary bladder structure, and decrease kidney weight [3]. Considering their significant toxicity and potential mutagenicity, fungicides have received lots of attention all over the world [4]. Therefore, it is very important to develop an accurate and sensitive detection methodology for the simultaneous measurement of commonly used fungicides in fruits samples. The traditional analytical methods to test the fungicides in different fruits are usually based on liquid chromatography (LC) [5; 6; 7] and gas chromatography (GC) [8; 9; 10]. Multiple techniques have been employed for the quantitation of fungicides. The coupling of efficient LC or GC with mass spectrometry detector (LC-MS or GC-MS) had become a powerful tool for the separation of the target analytes and accurate qualitative analysis. Compared with GC-MS, LC-MS is more user friendly and is commonly applied for substances with low volatility and thermal instability [11; 12]. With the increasing qualitative and quantitative requirements, a general low resolution mass spectrometer could not confirm the exact structure of (semi) unknown compounds. The development of a high resolution mass spectrometer (HRMS) provides an effective approach to solve the above problems. It was often used in peptides sequencing [13; 14]; hence there is an increasing focus on and interest in investigating the quantification of small molecules [15; 16; 17]. The Orbitrap-based high resolution mass spectrometer (HRMS) is a very recent technique based on an Orbitrap mass spectrometer coalescing with the high resolution performance of the Orbitrap and the selectivity of the quadrupole [18]. This combination is a promising way to screen emerging pollutants in environmental and biological samples, which is combined with the high energy collision (HCD) cell. High quality MS and MS\({}^{2}\) spectra could be obtained, which is beneficial for further structural identification. However, matrix interference was universal during the LC-MS analysis; thus extraction and enrichment with high efficiency are increasingly indispensable prior to the instrumental detection. The research on highly efficient extraction materials has drawn much attention [19; 20; 21; 22]. Graphene oxide (GO), a derivate of graphene (G), can help to improve the adsorption of target compounds, owing to its unique structure. A large number of epoxide, hydroxyl, and carboxyl groups were distributed on the surface of a GO sheet, and it had a large, delocalized, \(\pi\)-conjugated structure that can lead to high adsorption efficiency and a strong affinity for compounds with hydrophobic properties or aromatic ring structures. This work has focused on the novel application of GO with magnetic solid phase extraction (MSPE). The introduction of magnetic composites into a GO sheet could combine the high adsorption efficiency of the GO sheet with convenience and fast magnetic separation. Recently, the preparation of magnetic GO composites with a convenient co-precipitation method or electrostatic interaction has been commonly researched [23; 24]. However, the magnetic GO composites prepared with these methods showed weak correlated driving force or physical force and showed unsatisfactorily acid-resistant natures.