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A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16−32 μm. This was accomplished by introducing N 2 into ICP to increase the sensitivity. The obtained U-Pb ages for zircon standards GJ-1, TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500. Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages. The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy, but it may yield artificial high precisions for single analyses. Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses. Calibration against the NIST glasses using Si as an internal standard, a systematic deviation of 10%−30% was found for most trace elements including Zr. However, the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g., BCR-2G, BHVO-2G and BIR-1G), or calibration against NIST SRM 610 and using Zr as an internal standard. Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti). Zircon, U-Pb age, trace element, uncertainty, LA-ICP-MS Citation: Liu Y S, Hu Z C, Zong K Q, et al. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS.

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The effects of adding nitrogen to the central gas flow (Ar + He) of an Ar plasma in laser ablation inductively coupled plasma mass spectrometry are presented. The optimum central gas flow rate was found to be negatively correlated with the N 2 gas flow rate. The addition of 5-10 ml min À1 nitrogen to the central channel gas in LA-ICP-MS increases the sensitivity for most of the 65 investigated elements by a factor of 2-3. The degree of enhancement depends, to some extent, on the 1st ionization energy. Another important advantage of N 2 mixed gas plasma for LA-ICP-MS is that the oxide ratios (ThO + / Th + ) are significantly reduced (one order of magnitude). The hydride ratio (ArH + /Ar + ) is also reduced up to a factor of 3, whereas the doubly charged ion ratio (Ca 2+ /Ca + ) is increased. The background signals at masses 29, 31, 42, 51, 52 and 55 are significantly increased due to the nitrogen based polyatomic interferences. Compared to the spatial profiles of the ion distributions in the normal mode (without nitrogen), the addition of 5 ml min À1 nitrogen leads to significant wider axial profiles and more uniform distribution of ions with different physical and chemical properties. Our results also show that the makeup gas flow (central channel gas) rate has a significant effect on the ion distribution of elements with different physical and chemical properties. A very consistent increase of argon signal by the addition of nitrogen (5 ml min À1 ) corroborates better energy transfer effect of nitrogen in the plasma.