Study On Heavy Metal Antagonism And Species Analysis In Selenium-rich Vegetables

Selenium-rich vegetables are popular now among the vegetable products, and have positive significance to the national health. However, there aren’t perfect laws and regulations as well as testing method about them. Under the situation of serious heavy metal compound pollution, how to make use of the antagonism of heavy metal to decrease the heavy metal content in selenium-rich vegetables becomes an urgent research topic. The toxicities of the heavy metals are closely related to their chemical forms. Therefore, in the heavy metal control process of the selenium-rich vegetables, we should not only test the total amount of the heavy metal, but we should also concern about its form to conduct further analysis. This thesis takes arsenic as an example to establish a testing method towards the five natural arsenides and three synthetic organic arsenics in selenium-rich vegetables. What’s more, a vegetable planting experiment is conducted to analyze the selenium concentration’s influence on vegetable growing, heavy metal antagonism and elements forms, etc. The main research results are as follows:1. The HPLC-ICP-MS technology is used to establish the testing method of five natural arsenides in selenium-rich vegetables. The ultrasonic heating extraction method is applied to extract the element under test in the samples, which highly improves the efficiency and results in a favorable extract effect. The ICP-MS condition optimized, and the RF power increased to1600%, the forms of arsenic are then fully disintegrated to meet the measurement requirements. The revolution speed of the peristaltic pump is increased to0.3r/min to coordinate with the velocity of the LC (Liquid Chromatogram). The mobile phase group becomes aqueous phase, so the temperature of the atomizing chamber should be set as4℃to decrease the disturb of the organic matter in sample solution to testing. An optimization is conducted to the chromatographic condition. Reverse phase anion chromatographic column is applied to conduct analysis, with ammonium nitrate solution of10mmol/L and diammonium phosphate solution of5mmol/L chosen as the mobile phase. The pH value is adjusted to9.2with ammonium hydroxide to conduct methods test. Through this method, the separation of five kinds of natural arsenic forms can be realized in25min, and the peak pattern is symmetrical and keen-edged with high sensitivity. Within0-100mg/L, each arsenic form enjoys favorable linear, with all of the correlation coefficients being higher than0.999.0.50,1.0and50.0μg/kg standard solutions are separately added in samples of selenium-rich garlic, the average recovery rate then is between89.5%and108.2%, with RSD (relative standard deviation) being0.68%-4.2%. The limits of quantitation of the five natural arsenic forms are0.2-0.5ng/mL.2. HPLC testing method of the three kinds of synthetic organic arsenic in selenium-rich vegetables is established. The pretreatment technology is optimized, and methanol+acetic acid (9/1, v/v) is chosen as the extractant, with copper sulfate being chosen as the protein precipitation solution. The condition of ultrasonic extraction under40℃within15min is confirmed. After standard addition recovery experiments, it is concluded that the recovery rate of the three kinds of synthetic organic arsenic is above80%. The chromatographic condition is optimized, and the C18reversed phase column is confirmed to be the analytical column. Water (2%acetic acid+0.26%triethylamine) and methyl alcohol are chosen as the mobile phase (with proportion being95:5) to conduct isocratic elution and complete separation of the three kinds of organic arsenic in15min. The method testing is conducted then:within0-60μg/mL, each organic arsenic form enjoys favorable linear, with all of the correlation coefficients being higher than0.999.5,10and20μg/kg standard solutions are separately added in samples of selenium-rich garlic, the average recovery rate is between89.5%and109.0%, with RSD (relative standard deviation) being1.7%-9.3%. The limit of quantitation of ROX is1.0μg/mL, ASA0.1μg/mL and NPA0.5μg/mL.3. The total selenium and heavy metal elements in the eight kinds of selenium-rich vegetables on sell are tested. There is no heavy metal found, which means that the heavy metal pollution of the selenium-rich vegetables on sell is well controlled, so they are edible. Through the vegetable growing experiment, the selenium’s influence on garlic growing is studied under the heavy metals compound pollution stress. From aspects such as total amount of heavy metal, forms of natural arsenic, conversion percent of organic selenium as well as content of vitamin C, the exogenous selenium’s influence on heavy metal antagonism and vegetable quality modification are studied.