Exploration Of Analyzing Methods In Re-Os Isotopic Dating And Calibration Of Os Reference Material

For the high quality data in low content of Osmium samples determined by ICP-MS, increasing the quantity of sample and reducing the volume of the absorption liquid were always employed. However, in this case, the acidity of the absorption liquid was too high to analysis by ICP-MS due to damage to cone. Because of Os serious memory effect, residual Os in sampling system would be superimposed to measurements of low content of Osmium samples. And the high acidity of the solution could easily lead to the loss of Os. Hence, the acidity control of the solution was necessary to ensure the accuracy of measured results.In this study, two methods to reducing the acidity of the absorbing liquid were discussed when analysis low Os content geological samples by means of a timing electronic control device-Carius tube in situ distillation Os.2.5 m L 10 mol/L Na OH solutions were added into the 8 m L dissolved solutions in carius tube prior to the situ distillation analysis for the low Os content geological samples. It could keep the acidity of the absorbing solution at 2%-3% with the high recovery of Os 90%±5%, which was affordable analysis by ICP-MS. The whole blanks obtained for Re and ¹⁸⁷Os value were 7.7 pg and 0.61 pg respectively with the separation of Re by anion exchange resin. The dating results obtained from reference materials GBW 04435（HLP） and GBW 04436（JDC） were 221.5±0.8 Ma（n=5） and 139.8±0.3 Ma（n=3）, which are respectively in good agreement with certified value of 221.4±5.6 Ma and 139.6±3.8 Ma.Synchronous two-stage for analysis of the low Os concentration in geological samples, The acidity of the absorbing solution could effectively be controlled between 2% to 3% with the recovery of Os 85%±5% which meets the requirements of ICP-MS measurements when 1.5 times volumes of ultra-pure water were added to the original solutions and gas flow were controlled between 45 to 55 m L/min. Used AG1-X8 resin to separation Re, 8 m L 6 mol/L HNO₃ could make Re eluted completely. This method is applied to analyze Re-Os dating of reference materials GBW04435（HLP）, the average model age was 219.4±2.1 Ma（n=9）, which was in agreement with the certified value of 221.4±5.6 Ma. The blank values of Re and ¹⁸⁷Os were 6.0 pg and 0.48 pg.The accuracy of calibration the osmium reverence material determines the accuracy of Os diluents. In this study, the method of demarcation Os reference material（NH₄）₂OsCl₆ was improved. The improved method was applied to calibration（NH₄）₂OsCl₆ which is from Alfa Aesar company. The percentage of Os in the（NH₄）₂OsCl₆ was 43.14%（n=3）, with the relative error of the theoretical value is 0.44%.