Effects of Iron-Calcium and Organic Matter Matrix on Cadmium Detection in Soil by Energy Dispersive X-Ray Fluorescence Spectroscopy

Cadmium (Cd) is a toxic and harmful heavy metal, and energy dispersive X-ray fluorescence spectroscopy (EDXRF) technology is widely used to detect Cd content in contaminated soil. However, matrix components such as coexisting elements and organic matter in soil may interfere with Cd detection results through X-ray absorption enhancement, spectral line overlap or scattering effect, and the influence of different soil components on the detection results has not been fully studied, which poses a challenge to the detection precision and accuracy of the instrument. Different concentrations of iron (Fe), calcium (Ca) and humic acid were added to diatomite as the matrix to evaluate the interference of these components on the Cd fluorescence signal, and the effects of overlapping interference deduction and correction methods on the Cd fluorescence intensity under different element content conditions were discussed. The results showed that the presence of Fe and Ca in the soil matrix (>5%) could lead to the underestimation of the EDXRF measurement of Cd through the inter-element absorption effect, while the presence of humic acid (>10%) could raise the low-energy scattering background in the spectral pattern and increase the determination error of low-concentration Cd. Based on the orthogonal experimental design, Fe, Ca and humic acid were introduced as correction factors, and a multiple linear regression correction model was established, which significantly improved the accuracy of EDXRF in determining Cd content in soil samples. The average relative error between the measured value of Cd content and the standard value decreased from 20.67% without correction to 7.64% after correction. This study demonstrates that the application potential of EDXRF technology in different types of soil through reasonable correction measures can be significantly improved, and an efficient, convenient and accurate detection method for environmental monitoring can be established.