Study On The Preparation Of UiO-66 And Its Application Of Adsorption, Elution And Quantification Of Total Arsenic In Rice

Arsenic is a highly toxic metalloid element, classified as type I category carcinogens by World Health Organization (WHO) and International Agency for Research on Cancer (IARC). The damage of arsenic on the human is a chronic, long-term process. Both of drinking water and food are the main sources of arsenic exporsure for public, where rice was consumed by more than 2.6 million people around the world as a staple food, particularly in majority of Asia countries. Meanwhile, rice has a stronger arseic bio-accumulative than other grains, which resulting in a higher content of arsenic. In high arsenic area such as Bangladesh, total arsenic content is up to 0.43 mg/kg, which seriously affecting the rice food security. Therefore, the research of arsenic in rice has important practical significance of the safety evaluation of arsenic. However, since the form of arsenic is not stable in rice and is easily affected by system matrix effects and other reasons, it is a bottleneck for the extraction, separation, enrichment and quantitative of arsenic from rice. Therefore, to establishment the detecting way of high selectivity, high sensitivity, low cost and easy operation for arsenic, is extremely important to the accurate quantification of total arsenic in rice. The key to the accurate quantification of total arsenic in rice is the effective and efficient separation of enrichment. UiO-66, is a new stable MOF material with features of large specific surface area, porosity, complex multi-node, etc. It also has superior water and thermal stability, and is easily synthesized, with low cost. It’s widely used in the heavy metals detection in the field of environmental protection of water environment and soil. But the reports of accumulation of heavy metals adsorption in food are less. Therefore, this article uses UiO-66 material to carry out the research of separation and enrichment of total arsenic in rice, and use hydride generation-atomic fluorescence spectrometry to quantify. Specific contents are as follows:(1) Hot solvent method was used to prepare UiO-66, which related qualities were tested by field emission scanning electron microscopy, X-ray powder diffraction, Fourier infrared spectrum,77 K N2 adsorption-desorption isothermal, thermo gravimetric analysis, chemical analysis. The results showed that the UiO-66 was a kind of positive hexagon with spatial octahedron cubic crystal structure and good topology structure. UiO-66 could form the octahedral UiO-66 secondary structural unit through the key with carboxyl and Zr-(u3)-O. The specific surface area, average pole diameter and volume of poles were 1009.3 m2/g,25.74 nm and 0.6496 cm3/g, respectively, which was an indication of good adsorption quality as a MOFs material. Also, UiO-66 has high thermal and chemical stability, which could not be collapsed till 400℃.(2) The effects of pH, adsorption temperatrue, adsorption ways and time on total arsenic adsorption by UiO-66 was studied. The results showed that the adsorption ratio could be achieved 99% at pH 6 and 20℃ for 60 μg/L after 5 min ultrasonic and 1 min votexing adsorption. While the desorption could be completed well to 99% with 5 mL 0.5 mol/L H3PO4 after 5 min ultrasonic and 1 min votexing treatment. At the same time, the adsorption process conform the Langmuir model which is the monolayer adsorption and pseudo-second order kinetic model.(3) The total arsenic was first extracted from certificated reference material rice flour by microwave assisted digestion in 7 mL 0.06 M HNO3-H2O2 at 180℃ for 20 min. UiO-66 was used to separate and enrich total arsenic under the optimized conditions, and then total arsenic was quantified by hydride generation atomic fluorecence spectrometry (HG-AFS). The total arsenic was 130.3 μg/L, the results was agreed well with the cetificated value (130 μg/L).(4) The application of UiO-66 for adsorption and enrichment of total arsenic and quantification by hydride generation atomic fluoerecence spectrometer in 7 kinds of actual rice samples. The results showed that this method can be effectively completed the separation, enrichment and quantification of total arsenic in rice, the recoveries between 90-110%, relative standard deviation was below 2%, and the limit of determination was 0.024 μg/kg...