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      激光微區原位Sr同位素分析
      發布時間: 2021-03-18 11:40:26來源:上譜分析瀏覽次數: 885
      測試項目:Sr同位素
      測試對象:長石、單斜輝石、磷灰石、碳酸鹽巖等
      測試周期:來電詳詢
      送樣要求:1、樣品靶或巖石薄片,薄片尺寸參見原位主微量元素分析要求;2、長石樣品Sr含量大于200ppm,單斜輝石樣品Sr含量大于80ppm;3、樣品貧Rb,Rb/Sr含量比低于0.1,大于此范圍的樣品請提前告知。
      完成標準:測試內精度及標樣外精度和準確度確保達到國際水平。

      方法描述:

      20.1長石,單斜輝石和磷灰石LA-MC-ICP-MS微區原位Sr同位素比值測試

      微區原位長石,單斜輝石和磷灰石Sr同位素比值測試在武漢上譜分析科技有限責任公司利用激光剝蝕多接收杯電感耦合等離子體質譜(LA-MC-ICP-MS)完成。激光剝蝕系統為Geolas HD(Coherent,德國),MC-ICP-MS為Neptune Plus(Thermo Fisher Scientific,德國)。8個法拉第杯(從L4到H3)被同時用于接收Kr,Rb,Er++,Yb++和Sr信號的離子信號。Jet+X錐組合被采用以提高儀器靈敏度。激光剝蝕系統使用氦氣作為載氣。分析采用單點模式,激光束斑大小根據樣品Sr信號強度調節,一般為60-160 μm。激光剝蝕速率為8-15 Hz。激光能量密度固定在~10.0 J/cm2。分析過程配備了信號平滑裝置以提高信號穩定性和同位素比值測試精密度(Hu et al. 2015)。全部分析數據采用專業同位素數據處理軟件“Iso-Compass”進行數據處理(Zhang et al., 2020)。Sr同位素干擾校正采用Tong et al.(2016)Zhang et al.(2018)的方法。校正首先扣除氣體背景Kr干擾。接下來校正方案為(1)監控167Er++, 173Yb++信號強度,利用Er和Yb天然豐度比值(Berglund and Wieser, 2011),扣除168Er++ 對84Sr,170Er++170Yb++85Rb,172Yb++86Sr,以及174Yb++87Sr的干擾;(2)監測85Rb信號強度,利用實驗獲得的經驗87Rb/85Rb比值和指數法則,校正87Rb對87Sr的干擾。經驗87Rb/85Rb比值通過測定高Rb且已知87Sr/86Sr組成的標準樣品獲得。Sr同位素儀器質量分餾校正通過指數法則校正,校正因子利用88Sr/86Sr = 8.375209估算獲得(Tong et al. 2016, Zhang et al. 2018)。
      兩個天然長石標樣,YG0440(鈉長石)和YG4301(鈣長石),作為未知樣品監控微區原位長石Sr同位素校正方法的可靠性。YG0440和YG4301的化學組成和Sr同位素組成參見Zhang et al.(2018)。
      一個天然單斜輝石標樣,HNB-8(Sr=89.2 µg g-1),作為未知樣品監控微區原位單斜輝石Sr同位素校正方法的可靠性。HNB-8的化學組成和Sr同位素組成參見Tong et al.(2016)。
      兩個天然磷灰石標樣,Durango和MAD,作為未知樣品監控微區原位磷灰石Sr同位素校正方法的可靠性。Durango和MAD的化學組成和Sr同位素組成參見Yang et al.(2014)。

      20.2 In situ Sr isotope analysis of feldspar, clinopyroxene and apatite by using LA-MC-ICP-MS

      Sr isotope ratios of feldspars, clinopyroxenes and apatites were measured by a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) in combination with a Geolas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China. The Neptune Plus was equipped with nine Faraday cups fitted with 1011 Ω resistors. The Faraday collector configuration of the mass system was composed of an array from L4 to H3 to monitor Kr, Rb, Er, Yb and Sr. The combination of the high-sensitivity X-skimmer cone and Jet-sample cone was employed. In the laser ablation system, helium was used as the carrier gas for the ablation cell. For a single laser spot ablation, the spot diameter ranged from 60 to 160 μm dependent on Sr signal intensity. The pulse frequency was from 8 to 15 Hz, but the laser fluence was kept constant at ~10 J/cm2. A new signal smoothing device (Hu et al. 2015) was used downstream from the sample cell to eliminate the short-term variation of the signal. All data reduction for the MC-ICP-MS analysis of Sr isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020). The interference correction strategy was the same as the one reported by Tong et al. (2016) and Zhang et al. (2018). Firstly, the regions of integration for both gas background and sample were selected. Following background correction, which removes the background Kr+ signals, no additional Kr peak stripping was applied. Interferences were corrected in the following sequence: (1) the interferences of 168Er++ on 84Sr, 170Er++ and 170Yb++ on 85Rb, 172Yb++ on 86Sr, and 174Yb++ on 87Sr were corrected based on the measured signal intensities of 167Er++, 173Yb++ and the natural isotope ratios of Er and Yb (Berglund and Wieser, 2011); (2) the isobaric interference of 87Rb on 87Sr was corrected by monitoring the 85Rb signal intensity and a user-specified 87Rb/85Rb ratio using an exponential law for mass bias. The user-specified 87Rb/85Rb ratio was calculated by measuring some reference materials with a known 87Sr/86Sr ratio. Following the interference corrections, mass fractionation of Sr isotopes was corrected by assuming 88Sr/86Sr = 8.375209 (Tong et al. 2016 and Zhang et al. 2018) and applying the exponential law.
      During the LA-MC-ICP-MS analysis, a synthesised clinopyroxene glass (CPX05G, Sr = 518 µg g-1) was used as monitor to verify the accuracy of the calibration method. Two silicate glasses of StHs6/80-G and T1-G (MPI-DING), that both have high concentration of Rb, were used to calculated a specified 87Rb/85Rb ratio for the Rb interference correction.
      Two natural feldspar megacrysts, YG0440 (albite) and YG4301 (anorthite) were used as the unknown samples to verify the accuracy of the calibration method for in situ Sr isotope analysis of feldspars. The chemical and Sr isotopic compositions of YG0440 and YG4301 have been reported by Zhang et al. (2018).
      A natural clinopyroxene megacryst (Cpx, HNB-8) with a low Sr concentration (89.2 µg g-1) was analyzed as the unknown sample for in situ Sr isotope analysis of Cpx samples. The chemical and Sr isotopic compositions of HNB-8 have been reported by Tong et al. (2016).
      Two natural apatites, Durango and MAD were used as the unknown samples for in situ Sr isotope analysis of apatites. The chemical and Sr isotopic compositions of Durango and MAD have been reported by Yang et al. (2014).
      References
      Hu, Z.C., Zhang, W., Liu, Y.S., Gao, S., Li, M., Zong, K.Q., Chen, H.H., Hu, S.H., 2015. “Wave” Signal-Smoothing and Mercury-Removing Device for Laser Ablation Quadrupole and Multiple Collector ICPMS Analysis: Application to Lead Isotope Analysis. Analytical Chemistry, 87(2), 1152–1157.
      Liu, Y.S., Gao, S., Hu, Z.C., Gao, C.G., Zong, K.Q. and Wang, D.B., 2010. Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen: U-Pb dating, Hf isotopes and trace elements in zircons of mantle xenoliths. Journal of Petrology, 51(1–2): 537–571.
      Tong X.R., Liu Y.S., Hu Z.C., Chen H.H., Zhou L., Hu Q.H., Xu R., Deng L.X., Chen C.F., Yang L., Gao S., 2016. Accurate determination of Sr isotopic compositions in clinopyroxene and silicate glasses by LA-MC-ICP-MS. Geostandards and Geoanalytical Research, 40(1): 85–99.
      Zhang, W., Hu, Z., Liu, Y., Wu, T., Deng, X., Guo, J., Han Zhao, 2018. Improved in situ Sr isotopic analysis by a 257 nm femtosecond laser in combination with the addition of nitrogen for geological minerals. Chemical Geology, 479: 10–21.
      Berglund M. and Wieser M.E. (2011) Isotopic compositions of the elements 2009 (IUPAC Technical Report). Pure and Applied Chemistry, 83, 397–410.
      Yang Y.H., Wu F.Y., Yang J.H., Chew D.M., Xie L.W., Chu Z.Y., Zhang Y.B., Huang C., 2014. Sr and Nd isotopic compositions of apatite reference materials used in U-Th-Pb geochronology. Chemical Geology, 385: 35–55.
      Zhang W., Hu Z.C., Liu Y.S. (2020). Iso-Compass: new freeware software for isotopic data reduction of LA-MC-ICP-MS. J. Anal. At. Spectrom., 2020, 35, 1087–1096.

       
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