In this work, a graphene oxide (GO)–functionalized molecularly imprinted polymer (MIP) (GO–MIPs) was prepared using a non-covalent molecular imprinting approach and applied to dispersive solid-phase extraction (DSPE) coupled with ultra-high-performance liquid chromatography with photodiode array detection (UPLC-PDA) to sensitively detect cefadroxil (FAD) in aqueous solution. FAD was used as a template to synthesize GO–MIPs, with 2-(trifluoromethyl) acrylic acid (TFMAA) and ethylene glycol dimethacrylate (EGDMA) as the monomer and cross-linker, respectively, in methanol. The GO–MIPs was eluted with acetic acid–methanol (20/80, v/v) and then characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and Raman spectroscopy. The selectivity of the GO–MIPs versus a graphene oxide–functionalized non-imprinted polymer (GO–NIPs) was confirmed based on the selectivity factors (SFs) using cefixime, cefoxitin sodium and ceftiofur hydrochloride as structural analogues of FAD. The efficiency of the synthesized GO–MIPs was evaluated through application of the proposed DSPE procedure. The influencing factors of DSPE, such as the sample pH, extraction time, desorption reagents and desorption time, were optimized, and the analytical performance of the developed DSPE-UPLC-PDA method was evaluated under the optimized conditions. Good linearity was obtained over 0.04–6.0 μg mL−1 (R2 = 0.9979), with a detection limit (S/N = 3) of 0.01 μg mL−1. Finally, the developed method was applied to determine the concentration of FAD in water samples, and the spiked average recoveries ranged between 72.5% and 104.8%. The GO–MIPs served as good carriers for the selective adsorption of FAD and showed promise for the preconcentration of FAD in complex samples.

•Porphyrin-functionalized Fe3O4-graphene oxide nanocomposite was used as the MSPE adsorbent.•Seven sulfonamides from environmental water samples were enriched for chromatographic analysis.•The adsorption mechanism of the prepared porphyrin-functionalized Fe3O4–GO material was investigated and predicted.In this work, a novel type of porphyrin-functionalized Fe3O4-graphene oxide (TCPP/Fe3O4-GO) nanocomposite was synthesized. The adsorption mechanism of the prepared TCPP/Fe3O4-GO material was investigated and predicted. The π–π stacking and electrostatic attraction between the positively charged analytes and the negatively charged porphyrin-functionalized Fe3O4-GO accelerated the electron transfer between the materials. In addition, to investigate the preconcentration of the prepared TCPP/Fe3O4-GO, it was used as a magnetic solid-phase extraction adsorbent for the preconcentration of seven sulfonamides (SAs) from environmental water samples. Parameters that significantly affected the extraction of the SAs onto the sorbent, such as the elution solvent, extraction time and elution time, were optimized. Under the optimal conditions, the SAs in the environmental water samples were effectively detected. The linear range for the seven SAs was 0.5–20 μg mL−1, and the limits of detection for all seven SAs were 0.2 μg mL−1. Good reproducibility was obtained, along with relative standard deviations that ranged from 0.01 to 8.25%. The present method was applied to the determination of SAs in tap and river water samples, and the recoveries were satisfactory (83.7–116.7%).

Molecularly imprinted polymers (MIPs) of dopamine (DA) were constructed on the surface of graphene oxide (GO), and attached inside the pores of hollow fibers (HFs) for the solid-phase microextraction (SPME) of DA. Scanning electron microscopy, thermogravimetric analysis and Raman spectroscopy indicated that GO–MIP composites were successfully synthesized and modified in the pores of HFs via ultrasonication. Compared with common HFs and HFs modified with non-imprinted polymers (GO–NIP/HF) using the same SPME procedures, the GO–MIP/HF composites showed the best efficiency for the extraction of DA. The selectivity of GO–MIP/HF was investigated based on the selectivity factor (F) using epinephrine and norepinephrine as the structural analogues of DA. The linear range of dopamine was 1.05 × 10−3 to 5.27 × 10−3 μmol mL−1, using this process with a detection limit of 2.64 × 10−4 μmol mL−1. The extraction procedure based on GO–MIP/HF was successfully used for the determination of DA in human serum and its hydrochloride injection, showing average recoveries of 83–96%. GO–MIP/HF was a good carrier for the selective adsorption of DA, and showed promise for the preconcentration of DA in real samples.

A facile approach was used to prepare Fe3O4–graphene oxide (Fe3O4–GO) nanocomposites, and the application of these nanocomposites was investigated in the magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography with diode-array detection (HPLC-DAD) of three sulfonamides (SAs) from water samples. The Fe3O4–GO nanocomposites possess the advantages of both GO and Fe3O4. The Fe3O4–GO nanocomposites were characterized by scanning electron microscopy and vibrating-sample magnetometry. Sulfadiazine (SDZ), sulfadimidine (SDD) and sulfathiazole (STZ) were selected as target analytes to validate the extraction performance of the Fe3O4–GO nanocomposites as a MSPE adsorbent. The results indicated that the limits of detection of these sulfonamides were in the range of 0.05–0.10 μg mL−1, that the recoveries ranged between 67.4% and 119.9%, and that the linearity (R2 > 0.9900) and precision (between 0.04% and 9.03%) were good. The developed method can be used to determine and monitor SA residues in environmental water samples.

•Magnetite/graphene oxide/chitosan composite was synthesized by novel route.•The composite was used as magnetic absorbent for protein enrichment.•The composite had excellent adsorption performance for protein enrichment.In this study, a facile and novel strategy was developed to fabricate magnetite/graphene oxide/chitosan (Fe3O4/GO/CS) composite, and the composite was used as a magnetic adsorbent for the enrichment of protein, and followed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) analysis. The phase composition, chemical structure and morphology of the composite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), transmission electron microscopy (TEM), scanning electronic microscope (SEM) and vibrating sample magnetometer (VSM). Protein cytochrome c was chosen as model target to evaluate the adsorptive property of Fe3O4/GO/CS. After enrichment procedure and magnetic separation, protein bounded with the material was analyzed by MALDI-TOF MS without desorption. The results indicated that Fe3O4/GO/CS composite exhibited a good adsorptive capacity for protein, and Fe3O4/GO/CS composite had a promising potential in magnetic separation research.

A solid-phase extraction (SPE) using graphene as adsorbent coupled with capillary zone electrophoresis method was developed for the determination of four sulfonamide residues (sulfadimidine, sulfadimethoxine, sulfathiazole and sulfadiazine) in meat sample. Several condition parameters, such as elution solvents and volumes, sample pH and sample volume were optimized to obtain high SPE recoveries and extraction efficiency. Intra-day precisions of sulfonamides were in the range of 2.5–2.6 % and the inter-day precisions of sulfonamides were in the range of 2.6–3.4 %. Recoveries were 60.9–66.6 % for sulfadiazine and 86.1–111.4 % for other three sulfonamides in spiked meat sample. The developed method was successfully applied for the determination of sulfonamides in meat samples.

A facile approach was used to prepare Fe3O4–graphene oxide (Fe3O4–GO) nanocomposites, and the application of these nanocomposites was investigated in the magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography with diode-array detection (HPLC-DAD) of three sulfonamides (SAs) from water samples. The Fe3O4–GO nanocomposites possess the advantages of both GO and Fe3O4. The Fe3O4–GO nanocomposites were characterized by scanning electron microscopy and vibrating-sample magnetometry. Sulfadiazine (SDZ), sulfadimidine (SDD) and sulfathiazole (STZ) were selected as target analytes to validate the extraction performance of the Fe3O4–GO nanocomposites as a MSPE adsorbent. The results indicated that the limits of detection of these sulfonamides were in the range of 0.05–0.10 μg mL−1, that the recoveries ranged between 67.4% and 119.9%, and that the linearity (R2 > 0.9900) and precision (between 0.04% and 9.03%) were good. The developed method can be used to determine and monitor SA residues in environmental water samples.

Molecularly imprinted polymers (MIPs) of dopamine (DA) were constructed on the surface of graphene oxide (GO), and attached inside the pores of hollow fibers (HFs) for the solid-phase microextraction (SPME) of DA. Scanning electron microscopy, thermogravimetric analysis and Raman spectroscopy indicated that GO–MIP composites were successfully synthesized and modified in the pores of HFs via ultrasonication. Compared with common HFs and HFs modified with non-imprinted polymers (GO–NIP/HF) using the same SPME procedures, the GO–MIP/HF composites showed the best efficiency for the extraction of DA. The selectivity of GO–MIP/HF was investigated based on the selectivity factor (F) using epinephrine and norepinephrine as the structural analogues of DA. The linear range of dopamine was 1.05 × 10−3 to 5.27 × 10−3 μmol mL−1, using this process with a detection limit of 2.64 × 10−4 μmol mL−1. The extraction procedure based on GO–MIP/HF was successfully used for the determination of DA in human serum and its hydrochloride injection, showing average recoveries of 83–96%. GO–MIP/HF was a good carrier for the selective adsorption of DA, and showed promise for the preconcentration of DA in real samples.