Detection Of Heavy Metals Cadmium And Lead In Four Season Cabbages By Dual Pulse Laser Induced Breakdown Spectroscopy

Vegetables is one of the largest crops except grain crop acreage,in recent years due to the problem of soil heavy metals and atmospheric pollution problem is increasingly serious,the heavy metal pollution caused by vegetables in planting and transportation is becoming increasingly serious.The traditional method of detecting heavy metals in vegetables requires complicated pretreatment process.The vegetables are fast in circulation and cannot be tested in green,fast and multi-element.Laser induced breakdown spectroscopy(LIBS)is a kind of atomic emission spectrometry,which can be used to detect in situ,multi-element and nonpollution.The paper introduced LIBS to the heavy metal Cd and Pb elements of vegetables simultaneously,and the main research contents were as follows:This paper first introduces the advantages and disadvantages of LIBS technology for the detection of heavy metals in vegetables.The heavy metal Cd and Pb elements in the typical four seasons Chinese cabbage in vegetables were used as the test target,and the target material was simply dehydrated,crushed and pressed.Secondly,the influence of laser energy on the time evolution of the target material plasma is investigated.The higher the energy is,the shorter the plasma annihilation time is,and the longer the plasma life is.In the same case,the plasma lifetime of the dual beam pulsed laser is longer than that of single-beam pulsed laser.Also found that the expansion of the plasma target material in 1~2?s is the biggest,applying the results to the LIBS system spectral acquisition delay time range selection of optimization,the optimized LIBS system's laser energy of A is 232.4 mJ,laser energy of B is 207.2 mJ,spectral acquisition delay time is 1.38 ?s.At the same time in order to reduce the LIBS detection limit of target material,introduced the microwave auxiliary equipment,compared the original LIBS system with microwave assisted LIBS system influence on the signal intensity of target size,the influence of microwave assisted increase amplitude is different for different elements,The overall spectral signal was enhanced,and the detection limit of Cd elements was reduced from 4.11mg/kg to 3.57mg/kg,and the detection limit of Pb elements was reduced from 3.58mg/kg to 3.19mg/kg.The optimized LIBS system was applied to the detection of heavy metal Cd and Pb elements in the four seasons Chinese cabbage,and qualitative and quantitative analysis of the LIBS intensity value and the mass fraction of Cd and Pb elements.The appropriate classification model can be used to effectively distinguish the samples of the pollution-free test from the samples contaminated by Cd and Pb,and the classification accuracy is 100%.In quantitative analysis,the correlate on coefficient of Cd element single variable and multivariable fitting is 0.8498 and 0.9844 respectively,and the correlation coefficient of Pb element single variable and multi-variable fitting is 0.6145 and 0.9965 respectively.Finally,the paper summarizes the whole thesis and puts forward the problems and prospect of LIBS in the research of heavy metal detection in vegetables.