With agaric as carbon source and urea as nitrogen source, this paper has successfully synthesized nitrogen-doped carbon quantum dots (N-CQDs) by simple one-step hydrothermal method. A series of analysis have been used to make characterization of the physical, chemical structures and optical performance of N-CQDs. The fluorescence stability was studied by examining the ionic strength, pH value and storage time and other conditions. The cytotoxicity and bacterial toxicity of N-CQDs were applied to biological imaging. Considering the quenching effect of 2,4-dinitrophenol (2,4 DNP) on the fluorescence generated by N-CQDs, N-CQDs have been used as fluorescence probe in detection of 2,4-DNP where N-CQDs showed high sensitivity, selectivity and strong disturbance resistance to 2,4-DNP based on the quenching mechanism of transfer of resonance energy. It can also be concluded that agaric-based N-CQDs can be used in bio-imaging due to a good inhibitory effect on but low toxicity to bacteria. Under the optimal experimental conditions, the probe has presented a good coefficient of determination (R2 = 0.9969) and a low limit of detection (15.78 nM). This method has been successfully applied to determine 2,4-DNP in environmental samples and provided a new idea for developing green and natural composite carbon materials.

A novel method for the determination of aflatoxins B1, B2, G1, and G2 (AFB1, AFB2, AFG1, AFG2) in animal feed samples based on magnetic solid-phase cleanup and novel pre-column derivatization has been developed. In this work, synthesized polyvinylpyrrolidone-coated Fe3O4 magnetic nanoparticles were applied as adsorbents for rapid cleanup for extracts of animal feed samples. The purified extract was then derivatized with trifluoroacetic acid coupling ultraviolet irradiation which enabled the weakly fluorescent AFB1 and AFG1 transformed into their highly fluorescent hemiacetals derivatives. Afterward aflatoxins were separated and quantified by reverse phase liquid chromatography with fluorescence detection. The results indicated that four AFs presented excellent linear response with correlation coefficients > 0.996 and recoveries ranged from 86.7 to 108.9% with relative standard deviations (RSDs) from 3.6 to 6.4%. The limits of detection (LODs) were 0.0392, 0.2429, 0.0842, 0.4556 ng mL-1 for AFB1, AFB2, AFG1 and AFG2, respectively.

A new method using nonanoic acid-coated magnetic Fe3O4 nanoparticles as adsorbent has been developed for the single-step extraction and preconcentration of lead and copper in tobacco samples. Transmission electron microscopy and X-ray diffraction spectrometry were used to characterize the adsorbent. The experimental parameters affecting extraction efficiency, including amount of nanoparticles, volume of chelating reagents, sample pH, ultrasonic time and desorption conditions were investigated. The analytes desorbed from nanoparticles were determined by flame atomic absorption spectrometry. Under the optimum conditions, good linearity was obtained in the range of 2-400 µg L-1 for copper and 5-800 µg L-1 for lead (r > 0.998, p < 0.05). The limits of detection for copper and lead were 0.2 and 0.5 µg L-1, with enrichment factors of 45 and 52, respectively. The method was successfully employed to tobacco sample analysis and got excellent recoveries between 89.2 and 100.7% with relative standard deviations (n = 6) of 4.5-5.9%.

Neste estudo, uma microextração em fase líquida suportada em fibra oca e com agitação vórtex (VA-HF-LPME) acoplada à cromatografia líquida de alta performance (HPLC) foi desenvolvida para a determinação de três compostos endócrinos sintéticos desreguladores [EDCs, bisfenol-A (BPA), bisfenol-AF (BPAF) e tetrabromobisfenol-A (TBBPA)] em amostras de leite. A agitação vórtex forneceu uma mistura efetiva e moderada das soluções de amostra e aumentou o contato entre os analitos e as camadas de fronteira da fibra oca, aumentando assim a razão de transferência de massa e levando à uma alta eficiência de extração dos analitos alvo. Os parâmetros que influenciaram o método de preparação da amostra do VA-HF-LPME, como os solventes orgânicos (fase aceptora), pH da solução da amostra (fase doadora), volume da amostra, concentração de NaOH, tempo de extração e força iônica, foram sistematicamente otimizados. As curvas de calibração instrumental do BPA, BPAF e TBBPA mostraram boas relações lineares (R² > 0,9988) na faixa de concentração de 0,5-200, 0,5-200 e 1,0-250 µg L-1, respectivamente. O desvio relativo padrão (RSD, n = 5) estava entre 1,3-3,7%. Os limites de detecção (LOD, S/N = 3) estavam na faixa de 0,16-0,35 µg L-1 e os limites de quantificação (LOQ, S/N = 10) na faixa de 0,51-1,12 µg L-1. O método proposto foi aplicado com sucesso na extração de EDCs em amostras de leite.

In this study, a vortex-assisted three-phase hollow fiber liquid-phase microextraction (VA-HF-LPME) coupling with high performance liquid chromatography (HPLC) method was developed for determination of three synthetic endocrine disrupting compounds[EDCs, bisphenol-A (BPA), bisphenol-AF (BPAF) and tetrabromobisphenol-A (TBBPA)] in milk samples. Vortex provided effective and mild mixing of the sample solution and increased the contact between analytes and boundary layers of the hollow fibre, thereby enhancing mass transfer rate and leading to high extraction efficiency of the target analytes. The influencing parameters of VA-HF-LPME sample preparation method, such as organic solvents (acceptor phase), pH of sample solution (donor phase), sample volume, concentration of NaOH, extraction time, and ionic strength were systematically optimized. The instrumental calibration curves of BPA, BPAF and TBBPA show good linear relations (R² > 0.9988) in the concentration range of 0.5-200, 0.5-200 and 1.0-250 µg L-1, respectively. The relative standard deviations (RSD, n = 5) were 1.3-3.7%. The limits of detection (LOD, S/N = 3) were in the range of 0.16-0.35 µg L-1 and the limits of quantification (LOQ, S/N = 10) were in the range of 0.51-1.12 µg L-1. The proposed method was successfully applied to the extraction of EDCs in milk samples.