High Precision Analysis of Pb Isotope Ratios Using MC-ICP-MS and the Pb Isotope Compositions of Soil Standard Materials
Lead isotope ratios for national soil reference materials was accurately determinated by us-ing multiple collectors inductively coupled plasma mass spectrometry(MC-ICP-MS).The fraction-ation properties of MC-ICP-MS in the determination of lead isotope was studied,which exhibits mass-independent fractionation.The Baxter and the standard-sample bracketing(SSB)method were used to corrected the mass-dependent fractionation and mass-independent fractionation in the instru-ment.The lead isotope ratio of the NIST SRM 981 standard solution which was corrected has high ac-curacy and precision.The lead isotope ratio of three national soil reference materials(GBW07564,GBW07406a,GBW07980)were determined using MC-ICP-MS,and the soil was digested by mi-crowave and purified.The recovery was more than 98％,and the blank of the whole process was less than 0.22 ng.The lead isotope ratio of GBW07564 is 19.960 3±0.030 3 for 206Pb/204Pb,15.767 5±0.006 1 for 207Pb/204Pb,and 39.086 8±0.026 4 for 208Pb/204Pb(n=9,2SD);the lead isotope ratio of GBW07 406a is 18.802 4±0.001 8 for 206Pb/04Pb,15.744 2±0.002 5 for 207Pb/204Pb,and 39.194 3±0.008 6 for 208Pb/204Pb(n=9,2SD);the lead isotope ratio of GBW07 980 is 18.614 2±0.005 7 for 206Pb/204Pb,15.737 8±0.004 4 for 207Pb/204Pb,and 38.962 9±0.015 3 for 208Pb/204Pb(n=9,2SD).The 206Pb/207Pb of these soil reference materials are 1.265 9±0.001 4,1.194 2±0.000 1,1.182 8±0.000 1(n=9,2SD),and the 208Pb/206Pb are 1.958 2±0.001 8,2.084 5±0.000 3,2.093 2±0.000 2(n=9,2 SD),respectively.These values are roughly within the range of natural soil lead isotopes 206Pb/207Pb(more than 1.17)and 208Pb/206Pb(less than 2.11).These samples are easily obtain-able,and their chemical and lead isotope compositions are uniform,making them suitable as isotope soil reference materials for monitoring the reliability of soil lead isotope chemistry and mass spectrom-etry analysis data.
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