测试项目：Pb同位素
测试对象：黄铁矿、黄铜矿、闪锌矿、方铅矿等
测试周期：来电详询
送样要求：1、样品靶或岩石薄片，薄片尺寸参见原位主微量元素分析要求；2、长石样品Pb含量大于5ppm，硫化物样品Pb含量大于200ppm；3、样品贫Hg，Hg/Pb含量比低于0.2，大于此范围的样品请提前告知。
完成标准：测试内精度及标样外精度和准确度确保达到国际水平。
方法描述：
18.1硫化物LA-MC-ICP-MS微区原位Pb同位素比值测试
微区原位硫化物Pb同位素比值测试在武汉上谱分析科技有限责任公司利用激光剥蚀多接收杯电感耦合等离子体质谱（LA-MC-ICP-MS）完成。激光剥蚀系统为Geolas HD（Coherent，德国），MC-ICP-MS为Neptune Plus（Thermo Fisher Scientific，德国）。激光剥蚀系统使用氦气作为载气。分析采用单点模式，激光的束斑大小和剥蚀频率根据样品的Pb信号强度调节，一般为44-90 μm和4-10 Hz。激光能量密度固定在~5.0 J/cm2。分析过程配备了信号平滑及“去汞”装置，该设备除了提高信号稳定性和同位素比值测试精密度外，还可以有效降低气体背景以及样品自身的Hg信号，确保204Pb的准确测定（Hu et al. 2015）。质谱仪Neptune Plus配备9个法拉第杯，可同时静态接收208Pb, 207Pb, 206Pb, 204Pb, 205Tl, 203Tl和 202Hg信号。单标Tl溶液通过膜去溶（Aridus II）引入，与激光剥蚀气溶胶颗粒混合后进入ICP，利用205Tl/203Tl比值完成对Pb同位素的实时仪器质量分馏校正。由于Tl元素和Pb元素在ICP中的质量分馏行为并不一致，因此采用两个硫化物标样MASS-1（USGS标样）和Sph-HYLM （闪锌矿，实验室内部标样）确定Tl和Pb的质量分馏关系，得到一个优化的且基体匹配的205Tl/203Tl比值。新的205Tl/203Tl比值取代了天然的205Tl/203Tl比值，并用于随后的实际硫化物样品Pb同位素分析。此外，残余的204Hg通过监控202Hg信号和利用202Hg/204Hg的天然比值（0.2301）获得。202Hg/204Hg的仪器质量分馏通过Tl同位素校正，并假设Hg和Tl的分馏因子一致。闪锌矿标样Sph-HYLM作为外标监控分析测试的精密度和准确度，208Pb/204Pb, 207Pb/204Pb, 和 206Pb/204Pb的长期测试准确度一般优于± 0.2 ‰，外部精度优于0.4 ‰ (2σ)。详细的仪器操作条件和分析测试方法可以参考Zhang et al. (2016) 。全部分析数据采用专业同位素数据处理软件“Iso-Compass”进行数据处理（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长石LA-MC-ICP-MS微区原位Pb同位素比值测试
微区原位长石Pb同位素比值测试在武汉上谱分析科技有限责任公司利用激光剥蚀多接收杯电感耦合等离子体质谱（LA-MC-ICP-MS）完成。激光剥蚀系统为Geolas HD（Coherent，德国），MC-ICP-MS为Neptune Plus（Thermo Fisher Scientific，德国）。法拉第杯和离子计数器被同时用于接收离子信号。其中208Pb，207Pb，206Pb用法拉第杯接收，而低信号204Pb和202Hg用离子计数器接收。激光剥蚀系统使用氦气作为载气。分析采用单点模式，激光的束斑大小和剥蚀频率根据样品的Pb信号强度调节，一般为90-160 μm。激光剥蚀速率为8-15 Hz。激光能量密度固定在~10.0 J/cm2。分析过程配备了信号平滑及“去汞”装置，该设备除了提高信号稳定性和同位素比值测试精密度外，还可以有效降低气体背景以及样品自身的Hg信号，确保204Pb的准确测定（Hu et al. 2015）。每次分析前，采用数个脉冲预剥蚀样品以消除样品表面Pb污染。在分析过程中，通过收集前20秒的背景数据获得来自气体背景中的Pb和Hg干扰信号，然后从样品信号中直接扣除。残余的204Hg通过监控202Hg信号和利用202Hg/204Hg的天然比值获得。202Hg/204Hg的仪器质量分馏通过背景中的Hg信号计算获得。Pb同位素的仪器质量分馏，仪器同位素比值漂移和任何系统性的离子计数器增益变化都采用SSB方法校正。BCR-2G和NIST 612被选择作为外标。一颗天然钾长石标样（Tuyk）作为未知样品监控数据质量。更详细的仪器操作条件和分析测试方法可以参考Zhang et al. (2016)。 全部分析数据采用专业同位素数据处理软件“Iso-Compass”进行数据处理（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.
