Homogeneity Test Of Geochemical Certified Reference Materials By X-Ray Fluorescence Spectrometry

Homogeneity test is an important step in the development of geochemistry certified reference materials.X-ray fluorescence spectrometry(XRF)is a common method to test the homogeneity of geochemistry certified reference materials.At present,the application of XRF to the homogeneity test of geochemical certified reference materials is still controversial in terms of minimum sampling mass.In this paper,the minimum sampling mass for homogeneity test of geochemistry certified reference materials was calculated by theoretical method.Under the condition that the samples are analysed as pressed powder pellets with a diameter of 30 mm,the theoretical minimum mass of Fe,Ti and Mn elements is 0.3259 g,0.1197g and 0.2615 g respectively,which is higher than the minimum sampling mass of 0.1 g as recognized by the general geochemical reference materials;and under the condition of 10 mm diameter,the theoretical minimum sampling mass of studied Si,Al,Fe,Mg,Ca,Na,K,Mn,Ti and P elements are all less than 0.1 g.Self-made sample preparation funnel by powder tablet pressing method,and the best sample preparation condition of 0.1 g sample is holding pressure for 1 min under 30 t pressure,and the samples diameter was about 12 mm.The optimum excitation voltage and current combination,spectrometer crystal,collimator and detector were studied.The best excitation currents and voltages combination of Fe-Ka and Mn-Ka were 60 kV-60 mA,Ti-Ka were 40 kV-90 mA,the rest were 30 kV-120 mA;Fe-ka,Mn-Ka and Ti-Ka adopted S2 collimator,the rest adopted S4 collimator;Fe-K?,Mn-Ka,Ti-K?,Ca-K? and K-K? adopted LiF(200)crystal,Si-Ka and Al-Ka adopted PET crystal,Mg-Ka and Na-Ka adopted RX25 crystal and P-Ka adopted Ge crystal;Fe-Ka and Mn-Ka adopted SC detector,the rest adopted PC detector.Using 32 first-class national geochemistry certified reference materials to make the standard curve,the Correlation Coefficients of the standard curve were 0.9943?0.9997.Self-made platinum-gold crucible for melting sample preparation,and the optimal melting conditions of 0.1 g sample were obtained:The ratio of sample to flux was 1:4(w/w),2 drops of 0.2 g/mL NH4I release agent,melting at 1050? for 10 minutes,and the diameter of samples was about 12 mm.Compared with the tablet pressing method,the optimized instrument conditions were slightly changed:All adopted S4 collimator,Si-Ka crystal changed into RX25 crystal,Ti-Ka detector changed into SC detector,PHA adjusted according to the actual situation.Using 32 first-class national standard materials to make the standard curve,the correlation coefficients of the standard curve were 0.9973?1.0000.Using wavelength dispersive XRF,two analytical methods of 10 components of 0.1 g SiO2,Al2O3,TFe2O3,MgO,CaO,Na2O,K2O,Mn,Ti and P were established.The homogeneity of GBW07425,GBW07428,GBW07388,GBW07375,GBW07378 and GBW07379 six geochemical reference materials was examined at the minimum sampling mass.Each reference material was taken from 15 bottles,each bottle was sampled in 2 parts,and a total of 30 samples were made.The homogeneity of the samples was determined by the F value of one-way Anova,the standard deviation(s)of the measured value and the relative standard deviation(RSD%).The accuracy of the method in this study was high,the relative error of powder tablet pressing analytical method was less than 16%,the relative error of melting sample preparation method is no more than 9.1%;the precision was good,the RSD%of powder compression method is no more than 4.3%,and the RSD%of melting sample preparation method is no more than 7%.Compared the results of conventional sampling mass and minimum sampling mass,both of them were close to the standard values.The F values of the two sample preparation methods were less than the critical values,and the homogeneity of the reference materials was good.The results show that the proposed method of O.lg sample weighing can be applied to the homogeneity test of geochemical reference materials,which solves the problem of determining the minimum sample mass when XRF is used for homogeneity test.