Effect and Correction of Iron in Soil on Accuracy of Chromium Determination by Portable X-ray Fluorescence Spectrometry

BACKGROUND The portable X-ray fluorescence spectrometer (p-XRF) can detect chromium in soil rapidly, but its detection accuracy is low because of the complexity of soil composition and the unknown matrix effect. As the main element in soil matrix, iron content varies widely in different types of soil, which is one of the main elements affecting the accuracy of p-XRF determination of chromium. OBJECTIVES To improve the accuracy of p-XRF in the determination of chromium in soil. METHODS The relationship between the fluorescence intensity of chromium and the content of chromium and iron was studied by using artificial soil samples with added chromium and iron. A calibration model was established based on research results. RESULTS When the content of iron in the soil sample was fixed, the content of chromium changed linearly with its corresponding characteristic X-ray fluorescence intensity, and the correlation coefficients were all above 0.9990. Moreover, the growth rate of the fluorescence intensity of chromium increased with the increase of iron content in the soil. In addition, through the study of soil samples with the same chromium content and different iron content, the fluorescence enhancement effect of iron on chromium was verified, and it was found that the enhancement effect was also related to the interaction of iron and chromium. CONCLUSIONS Combining the research results of matrix effects of chromium and iron, the correction equation of effect of iron on p-XRF determination of chromium has been established. Compared with ordinary linear regression, the correlation coefficient of this method increased from 0.9011 to 0.9986. The average relative error for p-XRF analysis of diatomite samples decreased from 21.94% to 2.52%, and the average relative error of p-XRF analysis of actual soil samples decreased from 51.02% to 5.21%.