Studies On Determination Of Trace Lithium In Environmental And Geological Samples By Isotope Dilution High Resolution Inductively Coupled Plasma Mass Spectrometry

Based on sufficient literature investigation, the author has developed a set of systemic, fast, accurate and precise method of trace lithium determination combining Isotope Dilution and High Resolution Inductively Coupled Plasma Mass Spectrometry (ID-HR-ICP-MS). In the experiment, high-pressure, airproof,acid dissolution are adopted to digest all samples avoiding the contamination and losses of lithium. The improved pressurized (depressurized) micro chromatogram separation techniques are applied to improve the efficiency of separation and purity procedure. Using the column with 2.5mm inner diameter and the cation exchange resins (200 ~ 400 meshes), the whole separation process can be completed within 10 minutes. By this technique, the volume of eluting solutions is less than 2mL, and the matrix separation efficiency is higher than 95%; the purpose to set a simple, economical and high efficiency separation method is fulfilled. Moreover, factors influencing the separation effect have been studied, and the relevant parameters on separating lithium solutions are obtained.Before determining lithium isotope ratio by HR-ICP-MS, the parameters of operation and acquisition are optimized; the interferences in measuring progress (such as bi-charge ion interference, multi-atom ion interference, background spectrometry interference, matrix effects, memory effects, dead time and mass bias effects, etc.) are studied and corrected. Then, the precision and accuracy of isotope ratio determination are improved. To determinate a kind of natural lithium standard solution with the concentration of 1×10-8g/mL, the determination precision of 6Li/7Li is 0.38%. The determination limit of this method is 2.1×10-9 g/g(3σ), and the result precision of parallel samples is less than 3%. The concent of lithium in two geological reference materials(GSD-5, GSD-10) has been determined by ID-HR-ICP-MS. The results accord with reference values perfectly, which proving this method is effective and reliable, and can be applied to analyze trace lithium.To guarantee the quality of analysis, the uncertainty of the analysis of the result and the metrological characterization of the spike have been evaluated in internationally current ways. All the parameters needed for the calculation process have been collected and calculated, and a mathematical model has been set up. The results indicate that the spike has good traceability and metrological characterization. Individual contribution of various factors to the uncertainty is calculated. The contribution of uncertainty of the blend isotope ratios is the largest. So, the accuracy of the determination for the blend isotope ratios is the major factor in improving the accuracy of the method.