Hf同位素分析 同位素質譜儀

測試項目：Hf同位素比值分析

測試對象：巖石、土壤、沉積物、海水、地下水

測試周期：45-90個工作日，可提供樣品測試加急服務。

送樣要求：

完成標準：前處理在超凈室100級超凈臺內進行，保證監測空白及樣品無污染，標樣和重復樣在允許誤差范圍內。
標樣數據：

方法描述：
13.1全巖Hf同位素比值分析
全巖Hf同位素前處理和測試由武漢上譜分析科技有限責任公司完成。
前處理流程：
前處理在配備100級操作臺的千級超凈室完成。樣品消解：（1）將200目樣品置于105℃烘箱中烘干12小時；（2）準確稱取粉末樣品50-200mg置于Teflon溶樣彈中；（3）依次緩慢加入1-3ml高純HNO₃和1-3ml高純HF；（4）將Teflon溶樣彈放入鋼套，擰緊后置于190℃烘箱中加熱24小時以上；（5）待溶樣彈冷卻，開蓋后置于140℃電熱板上蒸干，然后加入1ml HNO₃ 并再次蒸干；（6）用2.0M HF溶解樣品，待上柱分離。化學分離：用離心機將樣品離心后，取上清液上柱。柱子填充LN-Spec樹脂。用3M HCl、6M HCl和 4M HCl+H₂O₂ （0.5%）淋洗去除基體元素。最終用2.0M HCl將Hf從柱上洗脫并收集。收集的Hf溶液蒸干后等待上機測試。
儀器測試流程：
Hf同位素分析采用德國Thermo Fisher Scientific 公司的MC-ICP-MS（Neptune Plus）。儀器配備9個法拉第杯接收器。¹⁷²Yb⁺、¹⁷⁴Hf⁺、¹⁷⁵Lu⁺、¹⁷⁶Hf⁺、¹⁷⁷Hf⁺、¹⁷⁸Hf⁺、¹⁷⁹Hf⁺、¹⁸⁰Hf⁺同時被L4、L3、L2、L1、C、H1、H2、H3等8個接收器接收。其中¹⁷² Yb⁺和¹⁷⁵Lu⁺被用于監控并校正¹⁷⁶Yb⁺和¹⁷⁶Lu⁺對Hf同位素的同質異位素干擾。MC-ICP-MS采用了Jet+X錐組合和干泵以提高儀器靈敏度。根據樣品中的Hf含量，50 µl/min-100 µl/min兩種微量霧化器被選擇使用。Alfa公司的Hf單元素溶液被用于優化儀器操作參數。Hf國際標準物質（JMC 475，100 µg/L）用于質量監控。數據采集由8個blocks組成，每個block含10個cycles，每個cycle為4.194秒。Hf同位素的儀器質量分餾采用內標指數法則校正（Russell et al. 1978）：

公式中i和j指示同位素質量數，R_m和R_T分別代表樣品的測試比值和參考值（推薦值），f指儀器質量分餾因子。¹⁷⁹Hf /¹⁷⁷Hf被用于計算Hf的質量分餾因子（0.7325，Lin et al. 2016）。由于前期有效的樣品分離富集處理，干擾元素Yb和Lu被分離干凈。殘留的¹⁷⁶Yb⁺和¹⁷⁶Lu⁺干擾校正采用Lin et al.（2016）校正方法。實驗流程采用兩個Hf同位素標樣（JMC 475和AlfaHf）之間插入7個樣品進行分析。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）。JMC 475的¹⁷⁶Hf /¹⁷⁷Hf分析測試值為0.282154±5（2SD, n=67）與推薦值0.282157±16（2SD）（Zhang and Hu 2020）在誤差范圍內一致，表明本儀器的穩定性和校正策略的可靠性滿足高精度的Hf同位素分析。
BCR-2（玄武巖）被選擇作為流程監控標樣。BCR-2的¹⁷⁶Hf /¹⁷⁷Hf分析測試值為0.282864±14（2SD, n=19），與推薦值0.282869±9（Zhang and Hu 2020）在誤差范圍內一致。數據表明，本實驗流程可以對樣品進行有效分離，分析準確度和精密度滿足高精度的Hf同位素分析。
本測試方法適用Hf 含量>2 ppm的巖石樣品，保證實際地質樣品測試內精度（2SE）=0.000005-0.000012（0.015‰~0.04‰，2RSE），測試準確度優于0.000012（~0.04‰）。Hf含量低于2 ppm的巖石樣品，測試精度和準確度會受到影響，影響程度受樣品Hf含量控制。低Hf樣品分析請事先咨詢技術人員，確保樣品分析質量。
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.