| It is one of most wide area and damaging environmental problems about soil heavy metal pollution in current. So the detection of heavy metals in soil has become an important work of environmental protection and agricultural production, but also the primary link with soil pollution control and remediation. EDXRF spectrometric has the advantages of high speed, high precision, simple operation, low cost, and can be used in detection at original space, which has been widely used in the field of heavy metal analysis. However, the quantitative analysis of heavy metals in soil is still in the exploratory stage. Due to the complexity of soil composition and the content of heavy metals low. So there is a lot of interference in the detection process. The research content is focused on how to reduce the detection limit of the method, correct matrix effect reasonable, and spectral line analysis. In this paper, the study focuses on the methods of reducing the detection limit and the method of matrix effect correction. The achievements of this study are as follows:(1)Intensity integral formula of relative strength and each important parameter was derived, and provided a theoretical basis in X-ray fluorescence analysis application on the fundamental parameter method.(2) The paper using MCNP simulation program to simulate the best condition of the detecting device: the distance between the detector and the sample is 0.8cm; the range of the incident angle and the exit angle is in the range of 45°~55° and 65°~75°, which provides a scientific basis for the design of X-ray fluorescence analysis in soil heavy metal detection application.(3)In this paper, the effect of element distribution on the fluorescence count is simulated and calculated by Monte Carlo Method. It draw a conclusion that the maximum depth and the thickness of the semi absorption layer can be detected about the five elements in the fluorescence analysis of Cr, Ni, Cu, Zn and As in the soil. This conclusion provides some reference value for the analysis of the distribution of heavy metal elements and the pollution assessment in the situ X-ray fluorescence analysis.(4) The program is designed to calculate the primary spectrum of X-ray tube by MATLAB programming in this paper. This program can quickly calculate primary spectrum data of silver target in 25 k V/45?A, it can provide data for the theoretical calculation of relative intensity.(5) According to the national standard GBW07401 and GBW07406 as an example, primary fluorescence intensity and two fluorescence intensity are analyzed respectively. In terms of soil matrix correction, the effect of the second fluorescence can be ignored, and only the absorption effect of the matrix is considered. It greatly simplifies the calculation of the fundamental parameter method for correcting the matrix effect.(6) In this paper, based on the analysis method of multiple standard samples, the calibration curve of the fundamental parameter method is established. The curve is the theory of relative strength and count rate curve. The comparative analysis the fitting degree of "theory is relatively strength and count rate curve" and "content and count rate curve". The improvement of fitting degree verifies the improvement of the fundamental parameter method to correct the matrix effect and the correctness of relative theoretically calculated intensities. The results show that using the analysis method of multi standard sample can obtain good analytical precision. |
PDF Full Text Request