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      激光微區原位Pb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: 674

      測試項目:Pb同位素
      測試對象:黃鐵礦、黃銅礦、閃鋅礦、方鉛礦等
      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Pb含量大于5ppm,硫化物樣品Pb含量大于200ppm;3、樣品貧Hg,Hg/Pb含量比低于0.2,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:

      18.1硫化物LA-MC-ICP-MS微區原位Pb同位素比值測試

      微區原位硫化物Pb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)。激光剝蝕系統使用氦氣作為載氣。分析采用單點模式,激光的束斑大小和剝蝕頻率根據樣品的Pb信號強度調節,一般為44-90 μm和4-10 Hz。激光能量密度固定在~5.0 J/cm2。分析過程配備了信號平滑及“去汞”裝置,該設備除了提高信號穩定性和同位素比值測試精密度外,還可以有效降低氣體背景以及樣品自身的Hg信號,確保204Pb的準確測定(Hu et al. 2015)。質譜儀Neptune Plus配備9個法拉第杯,可同時靜態接收208Pb, 207Pb, 206Pb, 204Pb, 205Tl, 203Tl和 202Hg信號。單標Tl溶液通過膜去溶(Aridus II)引入,與激光剝蝕氣溶膠顆?;旌虾筮M入ICP,利用205Tl/203Tl比值完成對Pb同位素的實時儀器質量分餾校正。由于Tl元素和Pb元素在ICP中的質量分餾行為并不一致,因此采用兩個硫化物標樣MASS-1(USGS標樣)和Sph-HYLM (閃鋅礦,實驗室內部標樣)確定Tl和Pb的質量分餾關系,得到一個優化的且基體匹配的205Tl/203Tl比值。新的205Tl/203Tl比值取代了天然的205Tl/203Tl比值,并用于隨后的實際硫化物樣品Pb同位素分析。此外,殘余的204Hg通過監控202Hg信號和利用202Hg/204Hg的天然比值(0.2301)獲得。202Hg/204Hg的儀器質量分餾通過Tl同位素校正,并假設Hg和Tl的分餾因子一致。閃鋅礦標樣Sph-HYLM作為外標監控分析測試的精密度和準確度,208Pb/204Pb, 207Pb/204Pb, 和 206Pb/204Pb的長期測試準確度一般優于± 0.2 ‰,外部精度優于0.4 ‰ (2σ)。詳細的儀器操作條件和分析測試方法可以參考Zhang et al. (2016) 。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)。

      18.2 In-situ Pb isotope analysis of sulfide by using LA-MC-ICP-MS

      In situ lead isotope analyses of sulfide were performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) equipped with a Geolas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China. In the laser ablation system, helium was used as the carrier gas for the ablation cell and was mixed with argon (makeup gas) after the ablation cell. The spot diameter ranged from 44 to 90 μm dependent on Pb signal intensity. The pulse frequency was from 4 to 10 Hz, but the laser fluence was kept constant at ~5 J/cm2. A new signal-smoothing and mercury-removing device was used downstream from the sample cell to efficiently eliminate the short-term variation of the signal and remove the mercury from the background and sample aerosol particles (Hu et al. 2015). The Neptune Plus was equipped with nine Faraday cups fitted with 1011Ω resistors. Isotopes 208Pb, 207Pb, 206Pb, 204Pb, 205Tl, 203Tl, and 202Hg were collected in Faraday cups using static mode. The mass discrimination actor for Pb was determined using a Tl solution nebulized at the same time as the sample, using an Aridus II desolvating nebulizer. The mass fractionation of Pb isotopes was corrected by 205Tl/203Tl with the exponential law. Note that the optimized values of 205Tl/203Tl, which were calibrated from measuring two Pb isotope standards MASS-1 (USGS) and Sph-HYLM (sphalerite, in-house standard), replaced the natural Tl isotopic composition for the mass fractionation correction of Pb isotopes. The 202Hg signal was used to correct the remaining 204Hg interference on 204Pb, using the natural 202Hg/204Hg ratio (0.2301). In addition, the mass fractionation of 204Hg/202Hg was corrected by the 205Tl/203Tl normalization. In this case, we assumed identical mass fractionation factors for 204Hg/202Hg and 205Tl/203Tl. Sph-HYLM was used to monitor the precision and accuracy of the measurements after ten sample analyses, over the entire period of analysis. The obtained accuracy is estimated to be equal to or better than ± 0.2 ‰ for 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb compared to the solution value by MC-ICP-MS, with a typical precision of 0.4 ‰ (2σ). The more detail of the in situ Pb isotopic ratios analysis was described in Zhang et al. (2016). All data reduction for the MC-ICP-MS analysis of Pb isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020).
      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.
      Zhang, W., Hu, Z.C., Gunther, D., Liu, Y.S., Ling, W.L., Zong, K.Q., Chen, H.H., Gao, S. and Xu, L., 2016. Direct lead isotope analysis in Hg-rich sulfides by LA-MC-ICP-MS with a gas exchange device and matrix-matched calibration. Analytica Chimica Acta, 948, 9–18.
      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.

      19.1長石LA-MC-ICP-MS微區原位Pb同位素比值測試

      微區原位長石Pb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)。法拉第杯和離子計數器被同時用于接收離子信號。其中208Pb,207Pb,206Pb用法拉第杯接收,而低信號204Pb和202Hg用離子計數器接收。激光剝蝕系統使用氦氣作為載氣。分析采用單點模式,激光的束斑大小和剝蝕頻率根據樣品的Pb信號強度調節,一般為90-160 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及“去汞”裝置,該設備除了提高信號穩定性和同位素比值測試精密度外,還可以有效降低氣體背景以及樣品自身的Hg信號,確保204Pb的準確測定(Hu et al. 2015)。每次分析前,采用數個脈沖預剝蝕樣品以消除樣品表面Pb污染。在分析過程中,通過收集前20秒的背景數據獲得來自氣體背景中的Pb和Hg干擾信號,然后從樣品信號中直接扣除。殘余的204Hg通過監控202Hg信號和利用202Hg/204Hg的天然比值獲得。202Hg/204Hg的儀器質量分餾通過背景中的Hg信號計算獲得。Pb同位素的儀器質量分餾,儀器同位素比值漂移和任何系統性的離子計數器增益變化都采用SSB方法校正。BCR-2G和NIST 612被選擇作為外標。一顆天然鉀長石標樣(Tuyk)作為未知樣品監控數據質量。更詳細的儀器操作條件和分析測試方法可以參考Zhang et al. (2016)。 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)。

      19.2 In situ Pb isotope analysis of feldspar by using LA-MC-ICP-MS

      Pb isotope ratios of feldspars were measured by a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) using a combination of Faraday cups and ion counters (FC-IC) 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. In the FC-IC array, 208Pb, 207Pb and 206Pb were measured using Faraday cups, and 204Pb and 202Hg were measured using three ICs mounted on the low mass Faraday cups. In the laser ablation system, helium was used as the carrier gas for the ablation cell and was mixed with argon (makeup gas) after the ablation cell. For a single laser spot ablation, the spot diameter ranged from 90 to 160 μm dependent on Pb 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 and mercury-removing device (Hu et al. 2015) was used downstream from the sample cell to eliminate the short-term variation of the signal and reduce the background of Hg in the carrier gas. Prior to data acquisition, an area slightly larger than the target area was gently pre-ablated for a few seconds to remove any surface Pb contamination. As stable background signals during analytical sessions were obtained, the Pb and Hg backgrounds were subtracted directly from the measured ion beam intensities during ablation. 202Hg ion signal was used to monitor the isobaric interference of 204Hg on 204Pb and a mass bias correction was applied to the 204Hg/202Hg ratio using the natural 204Hg/202Hg ratio (0.2301) and the exponential law factor calculated from the average values of the 204Hg/202Hg ratio in the gas background. A calibrator-sample-calibrator bracketing method was employed to correct for instrumental mass fractionation, instrumental drift and any systematic electron-multiplier gain bias. BCR-2G and NIST 612 were chosen as reference materials to correct the instrumental mass fractionation and the in-house reference of a K-feldspar megacryst (Tuyk) was used as the unknown sample to verify the accuracy of the calibration method. The more detail of the in situ Pb isotopic ratios analysis was described in Zhang et al. (2015). All data reduction for the MC-ICP-MS analysis of Pb isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020).
      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.
      Zhang W., Hu Z.C.,et al., Improved Inter‐calibration of Faraday Cup and Ion Counting for In Situ Pb Isotope Measurements Using LA‐MC‐ICP‐MS: Application to the Study of the Origin of the Fangshan Pluton, North China[J]. Geostandards and Geoanalytical Research, 2015, 39(4) : 467-487.
      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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