| Heavy metals can not be degraded by biology, and they can be enriched of thousands of times in the role of the food chain. Heavy metals can be taken into the plants through the soil, water, and air, and then were taken into the human body through the food chain, eventually it will cause harm to human health. Therefore, the determination of heavy metals is particularly important for human health. Maca (Lepidium meyenii Walp.) and Moringa(Moringa oleifera Lam.) can be used to treat disease, and they have gradually been used widely as the health care products. Tobacco was consumed a lot as an important industry in Yunnan. It is difficult to detect the heavy metal directly after sample digestion at trace levels due to their low concentration and impurity interference. Therefore, some extraction and preconcentration of the sample pretreatment techniques were necessary to improve the sensitivity and accuracy of detection. The adsorbent of magnetic solid-phase extraction were magnetic nanoparticles, they possess high surface area, and the diffusion distance is short. A low concentration of analyte can be extracted by using a small amount of adsorbent and shorter time, and a very high extraction capacity and extraction efficiency were achieved. In this paper, the heavy metals such as cadmium, lead, copper, nickel and cobalt in Maca, tobacco and Moringa were extracted and preconcentrated by magnetic solid-phase extraction, and the heavy metals were detected by flame atomic absorption spectrometry. The main research contents are as follows:Part 1 Multiwalled carbon nanotubes was modified by Fe3O4 nanoparticles as adsorbent of magnetic solid-phase extraction combined with flame atomic absorption spectrometry for the determination of in Cd(Ⅱ) and Pb(Ⅱ) in Maca(Lepidium meyenii)In this study, the surface of multiwalled carbon nanotubes was modified by Fe3O4 magnetic nanoparticles as the adsorbent of magnetic solid-phase extraction, and the modified nanomaterials as the adsorbent were used for adsorption and separation of Cd(Ⅱ) and Pb(Ⅱ) in Maca. The obtained optimal conditions as follows:the amount of adsorbent was 2.288 mg, the pH of the solution was 7.0, the adsorption time was 9.0 min, the 0.5 moL/L of HNO3 as the elution solvent, and the adsorbent was can be reused for 5 times. Under the optimum conditions, the calibration curve were linear in the range of 0.05-20 μg/mL for Cd and 0.05-25 μg/mL for Pb (R2>0.9986). The limit of detections were observed for Cd(Ⅱ) and Pb(Ⅱ) as 0.32 μg/L and 0.57 μg/L. The proposed method was effectively applied for determination of Cd and Pb in maca samples and satisfactory recoveries in the range of 94.8%-105.6% were achieved. The relative standard deviation (RSD) was 1.5%-2.5%(n= 6). The method is simple, accurate, cheap, and environment-friendly.Part 2 Fe3O4 nanoparticles coated with SiO2 and modified by APDC as adsorbent of magnetic solid-phase extraction combined with flame atomic absorption spectrometry for the determination of in Cu(Ⅱ) and Ni(Ⅱ) in tobacco samplesFe3O4 nanoparticles coated with SiO2 and modified with ammonium pyrrolidine dithiocarbamate as a new adsorbent for the single-step extraction and pre-concentration of trace amounts of copper and nickel from tobacco samples. The purpose of this work was to develop a simple, rapid and low-cost sample treatment suitable to assess the amount of heavy metals in tobacco which influence the health of human. The obtained optimal conditions as follows:the amount of APDC (100 μg/ml) was 150 μL; the amount of sorbent was 2.9 mg; the pH of the solution was 5.0; the adsorption time was 6.0 min; the 2.0 mL of acetonitrile as the elution solvent; and the adsorbent was can be reused for 3 times. Under the optimum conditions, the linear ranges were 0.02-15 mg/L for Cu and 0.02-20 mg/L for Ni (R2>0.9992). The method detection limit were 0.0028 μg/g for Cu and 0.0037 μg/g for Ni. The proposed method was effectively applied to analysis of Cu and Ni in tobacco samples and got excellent recoveries in the range of 89.6%-102.3%, and the relative standard deviations (RSD, n = 5) were 1.2%-2.5%. Compared with the traditional solid-phase extraction, this method was accomplished in 6 min, which greatly reducing the extraction time. Part 3 Fe3O4 nanoparticles was modified by oleic acid as adsorbent of magnetic solid-phase extraction combined with flame atomic absorption spectrometry for the determination of in Cd(Ⅱ), Pb(Ⅱ) and Co(Ⅱ) in Moringa Oleifera samplesIn this study, the surface of Fe3O4 nanoparticles with a magnetic core was modified by oleic acid as the sorbent of magnetic solid-phase extraction, and they were used for extraction of cadmium, lead and cobalt from Moringa oleifera samples. The particle size was 10-18 nm of the nanoparticles. The parameters affecting the preconcentration such as amount of nanoparticles, pH, adsorption time, coexisting ions, solution volume, eluent solution and reuse times have been studied in detail. Under the optimum conditions, the linearity obtained was in the range of 5.0-100.0 μg/L for three kinds of heavy metals and the squared regression coefficients were ranging from 0.9989 to 0.9999. The limits of detection were 0.09,0.26 and 0.54 μg/L for Cd(Ⅱ), Pb(Ⅱ) and Co(Ⅱ) ions, respectively. The relative standard deviations (RSD, n= 6) were less than 4.3%. The proposed method was effectively applied for the rapid extraction of Cd, Pb and Co from Moringa oleifera samples and satisfactory recoveries in the range of 90.0%-102.0% were obtained. |
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