Determination of Hf isotope ratios in zircon using multiple collector-inductively coupled plasma mass spectrometry equipped with laser ablation and desolvating nebulizer dual sample introduction system
2012 年 46 巻 1 号 p. 1-12
詳細
2012 年 46 巻 1 号 p. 1-12
We propose an analytical protocol for the accurate in situ determination of 176Hf/177Hf isotope ratios in zircon crystals by a 193 nm ultraviolet excimer laser ablation (193ExLA) multiple-collector inductively coupled plasma mass spectrometer (MC-ICPMS). Specifically, we used a simultaneous laser and dry solution aerosol dual sample introduction (DSI) system equipped with the 193ExLA-MC-ICPMS and an ARIDUS II desolvating nebulizer. The DSI-MC-ICPMS analyzed the laser aerosol from the zircon crystal while deionized water was aspirated from the ARIDUS II. Hf standard solutions were analyzed using the ARIDUS II with the laser switched off. This technique provides the same analytical conditions for both the laser and solution aerosols minimizing changes in the plasma condition. Therefore, the instrumental mass bias correction using a standard solution is accurately achieved. The instrumental mass bias for 176Hf/177Hf was corrected by measuring 179Hf/177Hf. 176Yb interference correction on 176Hf was performed using the 176Yb/173Yb ratio with a 173Yb/171Yb internal mass bias correction for Yb. Similarly, 176Lu interference was adjusted for using 176Lu/175Lu with 173Yb/171Yb or 179Hf/177Hf external mass bias correction. These correction factors were carefully determined using standard solutions. The correction factors were stable over three months, as observed by our routine monitoring. Standard zircons of 91500, TEMORA 2, Plešovice, and FC-1 were analyzed using 193ExLA with laser fluence at 20 J/cm2 and a repetition rate of 5-10 Hz. The ablation conditions resulted in craters of 40 μm diameter and 40 μm depth after a few minutes. Standard bracketing using JMC475 solution was applied every one to five spot laser analyses, thereby correcting for any remaining instrumental mass bias. The resultant 176Hf/177Hf isotope ratios were all in excellent agreement with the isotope ratios reported by TIMS and by other LA-MC-ICPMS analyses.
