Accurate Determination of Zr Isotopic Ratio in Zircons by Femtosecond Laser Ablation MC-ICP-MS with “Wet” Plasma Technique

This work evaluates the use of femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry(fs-LA-MC-ICP-MS) for Zr isotopic analysis in zircons. The mass fractionation caused by instrumental mass discrimination was corrected by a combination of internal correction using Sr as an internal standard(coming from a NIST SRM 987 standard solution) and external correction using a matrix-matched standard. Several important instrument parameters were investigated, such as the effect of the addition of N;and "wet" plasma condition, the mass fractionation behaviors between Zr isotopes and Sr isotopes, the position effect in laser ablation cell and the effect of laser ablation parameters(laser spot size and energy density). The Zr isotope compositions of seven zircons(GJ-1, 91500, Ple?ovice, Rak-17, Paki, Aus and Mala) were determined by the developed fs-LAMC-ICP-MS and thermal ionization mass spectrometry(TIMS). Our fs-LA-MC-ICP-MS results for Zr isotope compositions agreed with TIMS analyses within analytical uncertainties, indicating the presented method is a suitable tool to resolve isotopic zoning in natural zircons. The results also suggest that GJ-1, 91500, Ple?ovice, Paki, Aus and Mala had the homogenous Zr isotope composition and could be considered as the potential candidates for the Zr isotope analysis in zircons, except Rak-17 which presented the large Zr isotope variation.

A new analytical mode and application of the laser ablation inductively coupled plasma mass spectrometer in the earth sciences

We proposed a new laser analytical mode,which used the high-frequency laser ablation to deliberately obtain the peak-shape signal profile,combined with the linear regression calibration(LRC)method to calculate elemental or isotopic ratios.In order to assess the performance of the new laser analytical mode for the application in the field of earth science,we systematically investigated the elemental quantitative analysis with high spatial resolution(10μm),rapid U-Pb dating in zircons and accurate Sr-Hf isotope analysis in geological samples.The new high-frequency laser analysis technology(20 Hz,100 pulses)reduced the limit of detection(LOD)of 25 elements to 0.005-0.16μg g^(-1) with crater diameters of 10μm,which are significantly lower(decrease to 2-20%)than previous researches.The quantitative analysis of five silicate glass reference materials showed that the precision and accuracy of the 25 trace elements(with the concentration ranging from 0.17 to 683μg g^(-1))were better than 16% and 15%,respectively.The new methods raised the analytical throughput of zircon U-Pb dating,Sr isotope ratios and Hf isotope ratios to 250 analyses per hour,144 analyses per hour and 120 analyses per hour in theory,while the analytical accuracy and precision were not affected.The detailed investigations showed that the proposed new laser analytical mode has good application effects in the field of earth sciences.