Hf同位素分析 同位素质谱仪

测试项目：Hf同位素比值分析

测试对象：岩石、土壤、沉积物、海水、地下水

测试周期：45-90个工作日，可提供样品测试加急服务。

送样要求：

完成标准：前处理在超净室100级超净台内进行，保证监测空白及样品无污染，标样和重复样在允许误差范围内。
标样数据：

方法描述：
13.1全岩Hf同位素比值分析
全岩Hf同位素前处理和测试由武汉上谱分析科技有限责任公司完成。
前处理流程：
前处理在配备100级操作台的千级超净室完成。样品消解：（1）将200目样品置于105℃烘箱中烘干12小时；（2）准确称取粉末样品50-200mg置于Teflon溶样弹中；（3）依次缓慢加入1-3ml高纯HNO₃和1-3ml高纯HF；（4）将Teflon溶样弹放入钢套，拧紧后置于190℃烘箱中加热24小时以上；（5）待溶样弹冷却，开盖后置于140℃电热板上蒸干，然后加入1ml HNO₃ 并再次蒸干；（6）用2.0M HF溶解样品，待上柱分离。化学分离：用离心机将样品离心后，取上清液上柱。柱子填充LN-Spec树脂。用3M HCl、6M HCl和 4M HCl+H₂O₂ （0.5%）淋洗去除基体元素。最终用2.0M HCl将Hf从柱上洗脱并收集。收集的Hf溶液蒸干后等待上机测试。
仪器测试流程：
Hf同位素分析采用德国Thermo Fisher Scientific 公司的MC-ICP-MS（Neptune Plus）。仪器配备9个法拉第杯接收器。¹⁷²Yb⁺、¹⁷⁴Hf⁺、¹⁷⁵Lu⁺、¹⁷⁶Hf⁺、¹⁷⁷Hf⁺、¹⁷⁸Hf⁺、¹⁷⁹Hf⁺、¹⁸⁰Hf⁺同时被L4、L3、L2、L1、C、H1、H2、H3等8个接收器接收。其中¹⁷² Yb⁺和¹⁷⁵Lu⁺被用于监控并校正¹⁷⁶Yb⁺和¹⁷⁶Lu⁺对Hf同位素的同质异位素干扰。MC-ICP-MS采用了Jet+X锥组合和干泵以提高仪器灵敏度。根据样品中的Hf含量，50 µl/min-100 µl/min两种微量雾化器被选择使用。Alfa公司的Hf单元素溶液被用于优化仪器操作参数。Hf国际标准物质（JMC 475，100 µg/L）用于质量监控。数据采集由8个blocks组成，每个block含10个cycles，每个cycle为4.194秒。Hf同位素的仪器质量分馏采用内标指数法则校正（Russell et al. 1978）：

公式中i和j指示同位素质量数，R_m和R_T分别代表样品的测试比值和参考值（推荐值），f指仪器质量分馏因子。¹⁷⁹Hf /¹⁷⁷Hf被用于计算Hf的质量分馏因子（0.7325，Lin et al. 2016）。由于前期有效的样品分离富集处理，干扰元素Yb和Lu被分离干净。残留的¹⁷⁶Yb⁺和¹⁷⁶Lu⁺干扰校正采用Lin et al.（2016）校正方法。实验流程采用两个Hf同位素标样（JMC 475和AlfaHf）之间插入7个样品进行分析。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）。JMC 475的¹⁷⁶Hf /¹⁷⁷Hf分析测试值为0.282154±5（2SD, n=67）与推荐值0.282157±16（2SD）（Zhang and Hu 2020）在误差范围内一致，表明本仪器的稳定性和校正策略的可靠性满足高精度的Hf同位素分析。
BCR-2（玄武岩）被选择作为流程监控标样。BCR-2的¹⁷⁶Hf /¹⁷⁷Hf分析测试值为0.282864±14（2SD, n=19），与推荐值0.282869±9（Zhang and Hu 2020）在误差范围内一致。数据表明，本实验流程可以对样品进行有效分离，分析准确度和精密度满足高精度的Hf同位素分析。
本测试方法适用Hf 含量>2 ppm的岩石样品，保证实际地质样品测试内精度（2SE）=0.000005-0.000012（0.015‰~0.04‰，2RSE），测试准确度优于0.000012（~0.04‰）。Hf含量低于2 ppm的岩石样品，测试精度和准确度会受到影响，影响程度受样品Hf含量控制。低Hf样品分析请事先咨询技术人员，确保样品分析质量。
13.2 Scheme for Hf isotope ratio analyses using MC-ICP-MS
All chemical preparations were performed on class 100 work benches within a class 1000 over-pressured clean laboratory. Sample digestion: (1) Sample powder (200 mesh) were placed in an oven at 105 ℃ for drying of 12 hours; (2) 50-200 mg sample powder was accurately weighed and placed in an Teflon bomb; (3) 1-3 ml HNO₃ ａnd 1-3 ml HF were added into the Teflon bomb; (4) Teflon bomb was putted in a stainless steel pressure jacket and heated to 190 ℃ in an oven for >24 hours; (5) After cooling, the Teflon bomb was opened and placed on a hotplate at 140 ℃ and evaporated to incipient dryness, and then 1 ml HNO₃ was added and evaporated to dryness again; (6) The sample was dissolved in 2.0 M HF. Column chemistry: After centrifugation, the supernatant solution was loaded into an ion-exchange column packed with LN-Spec resin. After complete draining of the sample solution, columns were rinsed with 3 M HCl, 6 M HCl and 4 M HCl+H₂O₂ (0.5%) to remove undesirable matrix elements. Finally, the Hf fraction was eluted using 2.0 M HCl and gently evaporated to dryness prior to mass-spectrometric measurement.
Hf isotope analyses were performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich, Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China. The Neptune Plus, a double focusing MC-ICP- MS, was equipped with seven fixed electron multiplier ICs, and nine Faraday cups fitted with 10¹¹ Ω resistors. The faraday collector configuration of the mass system was composed of an array from L4 to H4 to monitor ¹⁷²Yb⁺、¹⁷⁴Hf⁺、¹⁷⁵Lu⁺、¹⁷⁶Hf⁺、¹⁷⁷Hf⁺、¹⁷⁸Hf⁺、¹⁷⁹Hf⁺、¹⁸⁰Hf⁺. The large dry interface pump (120 m³ hr^-1 pumping speed) and newly designed X skimmer cone and Jet sample cone were used to increase the instrumental sensitivity. Hf single element solution from Alfa (Alfa Aesar, Karlsruhe, Germany) was used to optimize instrument operating parameters. An aliquot of the international standard solution of 100 μg L⁻¹ JMC 475 was used regularly for uating the reproducibility and accuracy of the instrument. The Hf isotopic data were acquired in the static mode at low resolution. The routine data acquisition consisted of ten blocks of 10 cycles (4.194 s integration time per cycle). The total time of one measurement lasted about 7 min.
The exponential law, which initially was developed for TIMS measurement (Russell et al. 1978) ａnd remains the most widely accepted and utilized with MC-ICP-MS, was used to assess the instrumental mass discrimination in this study. Mass discrimination correction was carried out via internal normalization to a ¹⁷⁹Hf /¹⁷⁷Hf ratio of 0.7325 (Lin et al. 2016). The interference elements Yb and Lu have been completely separated by the exchange resin process. The remaining interferences of ¹⁷⁶Yb⁺ ａnd ¹⁷⁶Lu⁺were corrected based on the mothed described by Lin et al. (2016). One Alfa Hf standard was measured every seven samples analyzed. All data reduction for the MC-ICP-MS analysis of Hf isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020). Analyses of the JMC 475 standard yielded ¹⁷⁶Hf /¹⁷⁷Hf ratio of 0.282154±5（2SD, n=67）, which is identical within error to their published values (0.282157±16, Zhang and Hu 2020). In addition, the USGS reference materials BCR-2 (basalt) yielded results of 0.282864±14（2SD, n=19） for ¹⁷⁶Hf /¹⁷⁷Hf, respectively, which is identical within error to their published values (Zhang and Hu 2020).
References
Lin J., Liu Y.S., Yang Y.H., Hu Z.C. (2016). Calibration and correction of LA-ICP-MS and LA-MC-ICP-MS analyses for element contents and isotopic ratios. Solid Earth Sciences, 1, 5–27.
Russell, W.A., Papanastassiou, D.A., Tombrello, T.A., (1978). Ca isotope fractionation on the earth and other solar system materials. Geochim. Cosmochim. Acta, 42 (8), 1075–1090.
Zhang W., Hu Z.C. (2020). Estimation of isotopic reference values for pure materials and geological reference materials. At. Spectrosc. 2020, 41 (3), 93–102.
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.