Research And Application Of Total Reflection X-ray Fluorescence Technique For Quantitative Analysis Of Aquatic Plants

With the development of industry,environmental pollution has become more and more serious.The harmful heavy metals can migrate in water and soil and participate in the food chain cycle,which seriously affects human health.Therefore,real-time monitoring of harmful heavy metals in the environment is particularly important.Total reflection X-ray fluorescence(TXRF)spectroscopy was widely used in the fields of environment,biomedicine,food,criminal investigation and semiconductor materials because of its many advantages such as multi-element simultaneous detection,simple quantification,good economy and short analysis time.Due to the strong ability of aquatic plants to enrich heavy metals in water,they could combine with TXRF to monitor various elements in plant samples,which was of great significance for the treatment of water pollution.The main research contents and results were as follows:The TXRF analysis of plant samples has the following problems.Due to the high concentration and low fluorescence yield of low atomic number elements(P,S,Cl,k and Ca),the attenuation and saturation effects of the characteristic fluorescence were more severe in the sample,which makes it difficult to accurately quantify.For that,this paper started with two aspects of spectrum analysis method and sample quantification method and improved the quantitative accuracy of low atomic number elements in the acquisition of element characteristic peak data and quantitative calculation.Besides,TXRF technology was used in this paper to explore the Cr enrichment law of various tissues of Eichhornia crassipes and the changes between the elements.Based on the enrichment experiment,an adsorption experiment of Eichhornia crassipes root samples on Cr(VI)was carried out,and its adsorption law was clarified.1.The spectrum analysis process was used to optimize the data acquisition process of the energy spectrum.The appropriate energy spectrum smoothing and baseline removal methods were used to reduce the influence of background noise and sample scattering background on energy spectrum data.Combined with the peak-seeking and peak-fitting program,the full-spectrum characteristic fluorescence peak data can be obtained.2.Using TXRF technology to track the changes of nutrient elements in various tissues of the aquatic plant Eichhornia crassipes under Cr(VI)stress environment.The results of the culture experiment of Eichhornia crassipes showed that the enrichment ability of Eichhornia crassipes was negatively correlated with the concentration of Cr(VI)in the culture medium,and the bioconcentration factor(BCF)and Cr(VI)concentration could use a power function for a perfect fit.Besides,the changes of nutrients in roots,stems and leaves were found during enrichment.3.Based on the culture experiment of Eichhornia crassipes,the exploratory experiment on the adsorption capacity of Cr(VI)by the root tissue of Eichhornia crassipes was carried out.The results of adsorption experiments shown that the root tissue of Eichhornia crassipes has certain adsorption advantages for the high concentration of Cr in the environment.When the concentration was greater than 40 mg/L,the removal rate R was linearly related to the concentration of Cr(VI)in the environment and the amount of the additive.Besides,the adsorption process of Cr(VI)on the root material of Eichhornia crassipes was following the Freundlich equation,which indicated that the adsorption process was a chemisorption process,and Cr(VI)is easily absorbed by the root tissue material of Eichhornia crassipes.4.A method for quantifying the elements in plant samples using Ar peak normalization was proposed.In this paper,the Ar peak normalization quantification was verified with theoretical and experimental aspects.From the theoretical point of view,it was clarified that the Ar characteristic peak was mainly derived from the optical path of the incident and reflected X-rays and the standing wave field formed by the incident and reflected X-rays.From the experimentally,the main contribution of the standing wave field formed by the incident and reflected X-rays to the characteristic peak of Ar was confirmed,and the influence of the type of reflector and the amount of sample deposited on the characteristic peak of Ar was excluded.The results showed that the Ar peak normalization quantification method has considerable accuracy and precision.In summary,this paper has systematically studied the quantitative accuracy problem that TXRF analysis technology faces in the analysis of plant samples.The spectrum analysis method,aquatic plant heavy metal enrichment experiments and quantitative method suitable for plant analysis were explored.A complete spectrum analysis program was established,and the enrichment experiment was used to grasp the change law of elements in Eichhornia crassipes with Cr enrichment.As an extension,a new quantitative analysis method was proposed,and the accuracy of the method was experimentally demonstrated,which effectively improved the problem of low atomic number elements quantitative deviation and improved the accuracy of TXRF analysis of plant samples.