Development And Application Of Calibration Standard For LA-ICP-MS Microanalysis Of Scheelite Sample

Laser ablation-inductively coupled plasma-mass spectrometry（LA-ICP-MS）technology has lots of advantages such as high sensitivity,low detection limit and in-situ micro-analysis of solid samples,so it is widely used in geology,metallurgy and other fields.However,there is no internationally recognized,homogeneous and comerically available calibration standards.Therefore,it is necessary to develop a calibration standard consistent with scheelite.The aim of this paper addressed the issues existing in LA-ICP-MS microanalysis of scheelite in the following aspects.1.Rare earth element doped NaY（WO₄）₂single crystal for LA-ICP-MS determination of rare earth elements in laser crystals.Three single crystals of NaY（WO₄）₂ doped with rare earth elements with nominal concentrations of 50,500 and 5000μg g^-1 were prepared.The homogeneityof rare earth elements distribution in the crystals was investigated by LA-ICP-MS technique.The results show that the rare earth elements distributed homogenously in NaY（WO₄）₂ crystal,and the RSD of the analysis signal of LA-ICP-MS line scanning is less than 8%,which can meet the requirements of representative sampling of LA-ICP-MS and can be used as a quantitative calibration standard to correct the concentration of rare earth elements in NaY（WO₄）₂ crystals.After optimization,⁸⁹Y was employed as the internal standard,and a fluence of 8 J cm^-2,a frequency of 8 Hz and a laser spot diameter of 60μm were used for microanalysis.2.Development of LA-ICP-MS calibration standards for microanalysis of scheelite doped with various concentration of rare earth elements.Three calcium tungstate single crystals doped with tnominal concentrations of 50,250 and 5000μg g^-1 were prepared by the Czochralski method.Their matrix composition was confirmed to be consistent with that of natural scheelite by EPMA,XRD,gravimetry and ICP-OES.LA-ICP-MS line scanning(scanning speed:10μm s^-1)mode was used to analyze of the synthesized calcium tungstate crystal calibration standards,and the RSD of signal fluctuation of each element was calculated,which indicated the homogeneity of element distribution in the calcium tungstate crystal calibration standards.The results showed that RSD in Ca W-0 was2.12%-3.49%,and that in Ca W-1 was 1.72%-2.67%.The content of Ca varies from 0.35%to0.56%,while the content of W ranges from 0.59%to 0.87%.It shows that the major elements and rare earth elements are homogeneously distributed in the crystals.The determination of reference concentration of rare earth elements in the crystals was carried out in four laboratories and by several analytical methods.The good linearity（R²>0.98）between the LA-ICP-MS signal intensity and the reference concentrations verified the accuracy of the determination of rare earth elements in the synthesized calcium tungstate crystal and further implies it can be accurately calibrated using anyone as a calibration standard and the others as the unknown samples.The concentration of rare earth elements in Ca W-0,Ca W-1 and Ca W-3 has a good linear relationship with the absorbance（transparency）of the crystal wafer（R²>0.998）,which verifies the quantitative correlation between the signal intensity of LA-ICP-MS and the absorbance（transparency）of the sample.3.Study and application of quantitative calibration standard for microanalysis of scheelite.Two single crystals Ca W-50 and Ca W-500 doped with～30 trace elements were prepared by the Czochralski method and systematically characterized.Trace elements and rare earth elements are homogeneouly distributed in the crystals,and representative sampling can be obtained for LA-ICP-MS microanalysis.The contents of Ca O in Ca W-50 and Ca W-500 are（20.10±0.11）%and（20.05±0.32）%,respectively,and the contents of WO₃are（78.86±0.51）%and（79.03±0.41）%respectively,which were consistent with the matrix of natural scheelite.The RSD of rare earth elements in Ca W-500 is 4.00%-9.27%,the RSD of Sr、Nb、Ta、Zr and Hf are 5.50%,5.38%,9.86%,9.80%and 11.51%,respectively.The RSD of rare earth elements in Ca W-50 is 4.10%～7.23%,and others.Time is limited,this part of the work needs to be further supplemented in the future research.