Application of the wavelength dispersive X-ray fluorescence technique to determine soil fluorine with consideration of iron content in the matrix

The suitability of the wavelength dispersive X-ray fluorescence (WD-XRF) technique for the quantitative analysis of fluorine in soil was assessed in this study. Fluorine standards for WD-XRF calibration with soil matrices consisting of SiO2, Al2O3, Fe2O3, and CaO were prepared by varying the concentrations of CaF2 as a source of fluorine. Based on the standard calibration, the limits of detection and quantification were calculated as 812 and 2690 mg-F/kg-solid (or 1.62 and 5.39 mg-F in absolute mass term), respectively. In addition, the fluorine intensities of the standard samples with high iron content increased significantly compared to those with low iron content. Because of proximity between F-Kα and Fe-Lα line, the higher iron content preferably helped increase background fluorine intensities. As a means to compensate for the iron interference effect in fluorine analysis, the correction factor (CF) (0.0045) was derived based on the slope ratios between the measured X-ray intensity at the Bragg angle of 43.174° and iron content in the standard sample. The soil fluorine concentration determined by WD-XRF after the CF adjustment exhibited a significantly high correlation with that of the classical alkali fusion-ISE analysis. These findings clearly demonstrated that the WD-XRF technique is reliable enough to allow an easy, precise, and rapid quantitative determination of fluorine in a solid sample (such as iron-bound soil) compared to conventional methods.