Determination of fluorine in calcium superphosphate by X-ray fluorescence spectrometry with powder pellet preparation
The determination of fluorine content in calcium superphosphate has guiding significance for the production and quality control of calcium superphosphate.In experiments,the samples were thoroughly dried and then crushed until the particle size was less than 74 μm.Boric acid was used for edging,and the sample was prepared at pressure of 35 t for 30 s.F-Kα was selected as the analytical line.The method for the determination of fluorine in calcium superphosphate by wavelength dispersive X-ray fluorescence spec-trometry(WDXRF)with powder pellet preparation was established.A large number of calcium superphos-phate samples were scanned by X-ray diffraction(XRD).The results showed that the phases in calcium su-perphosphate were mainly composed of calcium sulfate,calcium fluoride,and silicon dioxide.Therefore,the calcium superphosphate sample which was certified by ion selective electrode method was use as the matrix in experiments.Various amounts of calcium fluoride were added followed by uniform mixing using a three-dimensional sample mixer.A series of calibration samples with a certain gradient of fluorine content that could cover the range of fluorine content in the sample were obtained for the drawing of calibration curves.Therefore,the spectrum peak angles of fluorine in the calibration sample series and calcium superphosphate sample were always consistent.Moreover,the influence of matrix effect and mineral effect on the determi-nation could be reduced.Three calibration samples with different fluorine contents were selected and then mixed with a three-dimensional sample mixer for 5 min.The samples were determined in parallel for five times according to the experimental method.The results showed that the relative standard deviation(RSD,n=5)of the measurement values of fluorescence intensity was less than 3.0％,indicating that the uniform-ity of the calibration samples could meet the experimental requirements.The calibration curve of fluorine was prepared using the fluorine content as the horizontal axis and the corresponding fluorescence intensity as the vertical axis.The linear correlation coefficient was 0.999 6,and the limit of detection was 3 mg/kg.Three calcium superphosphate samples with different fluorine contents were determined according to the experimental method,and the RSDs(n=10)were between 1.4％and 3.1％.Three samples were also de-termined by fluoride ion selective electrode method for comparison.The results showed that the determina-tion values of two methods were basically consistent.
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