GAO Junli, FAN Xiaolong, ZHANG Hao, LIU Danna, BAO Xiangchun
The determination of strontium and barium in high-purity rare earth metals and their oxides by inductively coupled plasma mass spectrometry(ICP-MS) is susceptible to mass spectral interferences of isobar,polyatomic ions,and double charges.The interference of fifteen single rare earth elements(including yttrium,lanthanum,cerium,praseodymium,neodymium,samarium,europium,gadolinium,terbium,dysprosium,holmium,erbium,thulium,ytterbium,and lutetium) with strontium and barium was investigated in experiments.The results showed that yttrium,lanthanum,cerium,erbium and lutetium had mass spectral interference with partial isotopes of strontium and barium,and the isotopes without interferences could be selected for determination.However,ytterbium exhibited double charge interference with the isotopes of strontium,thus requiring matrix separation to eliminate the interference.Except for ytterbium,the rare earth metals and their oxides could be dissolved with nitric acid and hydrogen peroxide,and then directly determined by ICP-MS in 1%(volume fraction,the same below) nitric acid as medium.The metal ytterbium and its oxides were dissolved with nitric acid and hydrogen peroxide,then the matrix was separated using ammonia,and the filtrate was acidified with nitric acid for the determination of strontium and barium.The experiments showed that the recoveries of strontium and barium were 95%-101% with ammonia separation,the residual ytterbium in filtrate was less than 10.00 ng/mL,which had negligible influence on the determination results.Cerium oxide,terbium oxide,thulium oxide and ytterbium oxide were selected from light,medium and heavy rare earths,and the matrix solutions with different concentrations were prepared according to the selected dissolution method to investigate the matrix effect of measured elements and internal standard elements.The results showed that the matrix effects on strontium and barium were basically consistent with the internal standards of rhodium and cesium,respectively.Accordingly,a method for the determination of strontium and barium in high-purity rare earth metals and their oxides by ICP-MS was established.The linear range of strontium and barium was 0-25.00 ng/mL,and the correlation coefficients of calibration curves were all greater than 0.999 5.The limit of detection was 0.004 4-0.18 μg/g,and the limit of quantification was 0.014-0.62 μg/g.The reference materials of cerium oxide,europium oxide and terbium oxide were determined according to the experimental method,and the results were consistent with the standard values.The content of strontium and barium in high-purity metal yttrium,neodymium,samarium,terbium,cerium oxide,terbium oxide,thulium oxide and ytterbium oxide were determined.The relative standard deviation(RSD,n=11) of determination results was 6.2%-14.6%,and the recovery was 88%-114%.
