[Recent advances in sample preparation technologies for analysis of harmful substances in aquatic products]

Bisphenols in Aquatic Products from South China: Implications for Human Exposure

In this study, 245 representative samples of aquatic products were selected from local markets in Shenzhen by stochastic sampling. The samples comprised eight species and fell into three aquatic product categories: fish, crustaceans, and bivalves. A total of eight BPs were determined by liquid chromatography coupled with mass spectrometry, namely, bisphenol A (BPA), bisphenol AF (BPAF), bisphenol AP (BPAP), bisphenol B (BPB), bisphenol S (BPS), bisphenol P (BPP), bisphenol Z (BPZ), and bisphenol F (BPF). All BPs were detected in aquatic products, except for BPAF, indicating pervasive contamination by BPs in aquatic products. BPS demonstrated the highest detection rate both before and after enzymatic hydrolysis, whereas BPAP exhibited the lowest detection rate before enzymatic hydrolysis and BPB displayed the lowest detection rate after enzymatic hydrolysis. The concentration difference before and after enzymatic hydrolysis proved to be statistically significant. Moreover, 49-96% of BPs in aquatic products were found in the combined state, underscoring the essentiality of conducting detections on aquatic product samples following enzymatic hydrolysis. While the health risks associated with ingesting BPs residues through aquatic product consumption were found to be minimal for residents at risk of exposure, the results suggest the necessity for more stringent regulations governing the consumption of aquatic products.

[Sulfonated magnetic graphite carbon nitride solid-phase extraction-ultra performance liquid chromatography-tandem mass spectrometry for screening malachite green and leucomalachite green in freshwater fish]

Malachite green (MG) and its metabolite, leucomalachite green (LMG), exert toxic effects on the human body. The use of these dyes is illegal, but they are still detected in aquatic products. Freshwater fish are aquatic products with the high non-qualified rates. Therefore, the sensitive screening of MG and LMG in freshwater fish is of great importance to ensure the safety of aquatic products. Owing to the low contents of MG and LMG in fish and the complex matrix of actual samples, sample preparation is required before detection to purify impurities and enrich the target compounds. Graphite carbon nitride (GCN), a polymer material composed of C, N, and H, has good chemical and thermal stability, a large specific surface area, and a large number of active sites. It has a wide range of application prospects in adsorption and can be used in food safety testing when compounded with Fe3O4 to form magnetic graphite carbon nitride (MGCN). In this study, sulfonated magnetic graphite carbon nitride (S-MGCN) was prepared by further functionalizing MGCN with sulfonic acid. After characterization by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometry (VSM), a magnetic solid-phase extraction (MSPE) method based on S-MGCN was established to extract MG and LMG from freshwater fish. The targets were screened using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Following sulfonic acid functionalization, S-MGCN showed increased electrostatic interactions based on the MGCN adsorption mechanism, which includes hydrogen bonds and π-π interactions; thus, its adsorption efficiency was significantly improved. The matrix effects were -42.21% and -33.77% before functionalization, -11.40% and -7.84% after functionalization, thus confirming that S-MGCN has significant matrix removal ability. Given that S-MGCN demonstrated excellent efficiency as an MSPE adsorbent, the adsorption conditions for S-MGCN were optimized. The optimal conditions were as follows: adsorbent dosage, 15 mg; adsorption time, 2 min; solution pH, 5; and ionic strength, not adjusted. Under these conditions, the adsorption efficiency of S-MGCN could reach 94.2%. Different organic solvents were used to elute adsorbed MG and LMG, and the desorption efficiency peaked when 1%(v/v) ammonia acetonitrile was used as the elution solvent. The elution volume was also optimized, and a maximum desorption efficiency of 93.2% was obtained when 1 mL of 1%(v/v) ammonia acetonitrile was added to S-MGCN. The limits of detection (LODs) and quantification (LOQs) of the two targets were determined at signal-to-noise ratios (S/N) of 3 and 10, respectively. The LODs and LOQs were 0.075 μg/kg and 0.25 μg/kg, respectively. The linear ranges of the two target compounds were 0.25-20.0 μg/kg with correlation coefficients (r) greater than 0.998. To assess accuracy and precision, we prepared spiked samples at three levels (low, medium, and high) with six parallel samples per level (n=6). The recoveries ranged from 88.8% to 105.9%. The intra- and inter-day relative standard deviations were 5.4%-13.7% (n=6) and 3.3%-11.1% (n=3), respectively. Compared with the national standard method, the proposed method features simpler sample pretreatment procedures, less use of organic reagents (5 mL), and a shorter extraction time (2 min); moreover, the method does not require complicated elution steps, and the eluent can be directly analyzed by UPLC-MS/MS. The test results of actual samples were consistent with those obtained via the national standard method, thus confirming the practical feasibility of the developed method. The proposed MSPE method based on S-MGCN is an efficient and environmentally friendly method that could provide a new methodological reference for the sensitive screening of MG and LMG in actual samples.

[Solid phase microextraction-high performance liquid chromatography of fluorinated covalent organic polymer to determine eugenol anesthetics in aquatic products]

Fluorinated covalent organic polymers (F-COPs) constitute a new class of porous materials with a topological structure, large surface area, and potential superiority over other types of polymers in sample preparation. In this study, a F-COP was rapidly synthesized by a simple Schiff-based reaction using 2,3,5,6-tetrafluoroterephthalaldehyde (TFA) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as monomers, and by adding scandium (Ⅲ) triflate (Sc(OTf)3) as the metal catalyst at room temperature. The prepared F-COP was applied as a coating adsorbent for solid phase microextraction (SPME) to enrich three kinds of eugenol anesthetics in aquatic products. The extraction performance of an enrichment medium is an important factor for practical application in real analytical projects. This F-COP adsorbent with rich π-stacking electrons contained abundant phenyl rings and imine (-C=N) groups throughout the molecular framework. The adsorption mechanism was explored and discussed based on the π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to targets. The F-COP was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, and scanning electron microscopy (SEM). The results indicated that the novel F-COP-SPME bar exhibited a rough and porous surface structure, good preparation reproducibility, and high stability. High performance liquid chromatography (HPLC) was performed with an ultraviolet-visible (UV-vis) wavelength detector. A Diamonsil plus C18 column (250 mm×4.6 mm, 5 μm) was used as the analytical column. The mobile phase comprised 60% methanol and 40% ultrapure water, and was flowed at 0.800 mL/min. The injected volume of the sample was 20.0 μL. The column temperature was maintained at 30 ℃ and the detection wavelength was set to 280 nm. Further, the SPME conditions (including extraction time, stirring rate, desorption solvent, and desorption time) that influenced the extraction efficiencies of the eugenol anesthetics were investigated in detail. Thus, the optimized F-COP-SPME bar conditions were established as follows: extraction time: 30 min; stirring rate: 700 r/min; desorption solvent: acetonitrile; desorption time: 10 min. By combining F-COP-based SPME with HPLC-UV analysis, an effective method was developed for the extraction and determination of eugenol, eugenyl acetate, and methyl eugenol residues in aquatic products. The method demonstrated good linearity in the range of 10-1000 μg/L for eugenol and eugenyl acetate, and 10-1500 μg/L for methyl eugenol, with correlation coefficients (r2) greater than 0.9961, low limits of detection (2.9-4.5 μg/kg, S/N=3), and excellent precision (relative standard deviations lower than 8.7%, n=5). Finally, the method was applied for the effective extraction of three kinds of eugenol anesthetics from tilapia and shrimp samples. The obtained recoveries were in the range of 76.7%-98.7% and 80.3%-104% with relative standard deviations of 8.5%-11.8% and 8.6%-12.4% (n=5), respectively. These results demonstrated that the F-COP is promising for use as an adsorbent in SPME for the determination of eugenol anesthetics in aquatic products. The developed method was suitable for the qualitative and quantitative determination of three kinds of eugenol anesthetics in aquatic products, yielding a satisfactory purification effect and sensitivity.