The widespread use of antibiotics and their discharge in raw form lead to the deterioration of water quality, which gradually accumulates in the environment and passes through the food chain, posing a threat to public health and safety [1,2]. Sulfonamide antibiotics (SAs) are a class of important antibiotic drugs with antibacterial effects. They have broad-spectrum inhibitory effects on gram-positive and gram-negative bacteria and chemical inhibitory effects on Gram-induced infections and some protozoa [3]. They are commonly used to prevent infection, treat disease, and promote growth. They are often used in human and veterinary medicine to treat digestive, respiratory and skin infections, as well as coccidiosis in animals [4]. However, due to their excessive and irregular use, SAs are widely found in soil, sediment, and various aquatic environments, eventually leading to sulfanilamide residues in animals [5]. Moreover, SAs can accumulate in the environment and be transferred to the human body through the food chain. To ensure human health, it is necessary to develop a simple, accurate, and rapid assay for the detection of SAs in the environment and food.

Currently, the detection methods for SAs mainly include high-performance liquid chromatography [6,7], high-performance liquid chromatography‒mass spectrometry [8,9], and capillary electrophoresis [10,11]. The use of modern analytical instruments has further improved the sensitivity of these methods, but the interference of complex matrices in actual sample analysis and the fact that SAs usually exist at low concentrations have made it difficult to quantitatively detect SAs, resulting in sample pretreatment becoming extremely crucial. The main methods commonly used for the pretreatment of antibiotic samples of SAs include solid-phase extraction (SPE) [12], [13], [14], [15], magnetic solid-phase extraction (MSPE) [16], [17], [18], and dispersive solid-phase extraction (DSPE) [19,20]. MSPE has received special attention because of its advantages, such as rapid sorbent separation, high extraction efficiency, simple operation and low sorbent dosage [21].

Porous carbon, with its large specific surface area and pore volume, has promising applications in sample pretreatment techniques. Cheng et al. utilized porous carbon as a solid-phase microextraction (SPME) coating to detect chlorobenzenes (CBs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and phthalic acid esters (PAEs) in environmental water samples [22]. However, the use of porous carbon as an adsorbent usually requires centrifugation for separation, which is time-consuming. Based on the above findings, the formation of magnetic porous carbon (MPC) by loading magnetic nanoparticles on porous carbon can not only combine the advantages of porous carbon materials in terms of specific surface area, adsorption capacity and chemical stability but also facilitate the rapid magnetic separation of adsorbents after extraction [23]. Han et al. used magnetic porous carbon prepared by a combustion method combined with a solvothermal method to achieve magnetic solid-phase extraction of triazole fungicides [24]. Lin et al. prepared magnetic fluorinated porous carbon (M-FPC) with a high fluorine content and large specific surface area by carbonization and further fluorination of an Fe-Zr bimetallic organic framework and achieved dispersed solid-phase extraction of perfluorinated compounds [25]. Recently, our research group also constructed a highly sensitive detection method for four bisphenol substances (BPA, BPAF, TBBPA and BPS) in environmental samples based on magnetic porous carbon solid-phase extraction and coupled capillary electrophoresis [26]. The combination of PC and Fe3O4 particles can not only realize simple and fast separation of materials and pollutants through magnets but also ensure that the composite material retains the excellent performance of PC, making it a promising adsorbent [27].

The porous carbon produced by the pyrolysis of sodium citrate has the advantages of being relatively cheap, easy to obtain, not activated, easy to treat and stable. In this research, PC was prepared by high-temperature pyrolysis of sodium citrate and etching, and a magnetic composite (PC@Fe3O4) was synthesized by in situ growth of Fe3O4 on PC via a solvothermal method. The material was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, BET analysis, zeta potential measurements, and saturation magnetization analysis, which successfully confirmed the synthesis of the material and related properties. Adsorption kinetic models were used to evaluate the adsorption properties of the six SAs. By exploring and optimizing the extraction conditions, a sample pretreatment method for magnetic solid-phase extraction of SAs was established. Combined with the establishment and optimization of the capillary electrophoresis method, an economical, sensitive, rapid magnetic solid-phase extraction-capillary electrophoresis method was established for the determination of sulfonamides in environmental water and milk samples (Fig. 1). An analytical method based on PC@Fe3O4 magnetic solid-phase extraction coupled with capillary electrophoresis (MSPE-CE) for the detection of SAs has not yet been reported, which provides a new approach for the detection of SAs.