武漢上譜分析科技有限責(zé)任公司
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武漢上譜分析科技有限責(zé)任公司
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聯(lián)系我時(shí)，請(qǐng)告知來(lái)自 儀表網(wǎng)測(cè)試項(xiàng)目：Pb同位素比值分析測(cè)試對(duì)象：巖石、土壤、沉積物、海水、地下水測(cè)試周期：45-90個(gè)工作日，可提供樣品測(cè)試加急服務(wù)
測(cè)試項(xiàng)目：Pb同位素比值分析
測(cè)試對(duì)象：巖石、土壤、沉積物、海水、地下水
測(cè)試周期：45-90個(gè)工作日，可提供樣品測(cè)試加急服務(wù)。
送樣要求：
| 樣品類型 | 送樣要求 | 測(cè)試元素 | |||||||||||||
| 全巖、礦物、土壤 水系沉積物 | Pb＞2ppm，≥200目，2～5g 紙袋包裝，含硫化物樣品需提前說(shuō)明 | 208Pb/206Pb，207Pb/206Pb，208Pb/204Pb，207Pb/204Pb，206Pb/204Pb | |||||||||||||
完成標(biāo)準(zhǔn)：前處理在超凈室100級(jí)超凈臺(tái)內(nèi)進(jìn)行，保證監(jiān)測(cè)空白及樣品無(wú)污染，標(biāo)樣和重復(fù)樣在允許誤差范圍內(nèi)。
標(biāo)樣數(shù)據(jù)：
方法描述:
12.1全巖Pb同位素比值分析
全巖Pb同位素前處理和測(cè)試由武漢上譜分析科技有限責(zé)任公司完成。
前處理流程：
前處理在配備100級(jí)操作臺(tái)的千級(jí)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(shí)；（2）準(zhǔn)確稱取粉末樣品50-200mg置于Teflon溶樣彈中；（3）先后依次緩慢加入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(shí)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1.0M HBr溶解樣品，待上柱分離?；瘜W(xué)分離：用離心機(jī)將樣品離心后，取上清液上柱。柱子填充AG樹脂。用1.0M HBr淋洗去除基體元素。最終用6.0M HCl將Hf從柱上洗脫并收集。收集的Hf溶液蒸干后等待上機(jī)測(cè)試。
儀器測(cè)試流程：
Pb同位素分析采用德國(guó)Thermo Fisher Scientific 公司的MC-ICP-MS（Neptune Plus）。儀器配備9個(gè)法拉第杯接收器。204（Pb+Hg）、206Pb、207Pb、208Pb、203Tl、205Tl和202Hg同時(shí)被7個(gè)接收器接收。其中202Hg被用于監(jiān)控并校正204Hg對(duì)204Pb同位素的同質(zhì)異位素干擾，204Hg/202Hg天然比值采用0.2301。MC-ICP-MS采用了Jet+X錐組合和干泵以提高儀器靈敏度。根據(jù)樣品中的Pb含量，50 µl/min-100 µl/min兩種微量霧化器被選擇使用。Alfa公司的Pb單元素溶液被用于優(yōu)化儀器操作參數(shù)。Pb國(guó)際標(biāo)準(zhǔn)溶液NIST 981 （200µg/L）作為質(zhì)量監(jiān)控和外部校正標(biāo)樣，208Pb的信號(hào)一般高于6V。每個(gè)標(biāo)樣和樣品中加入一定量的Tl溶液（NBS SRM 997），205Tl信號(hào)控制在4-5之間。Tl拖尾對(duì)204Pb的干擾沒有被觀察到。數(shù)據(jù)采集由8個(gè)blocks組成，每個(gè)block含10個(gè)cycles，每個(gè)cycle為4.194秒。Pb同位素的儀器質(zhì)量分餾采用假內(nèi)標(biāo)指數(shù)法則校正（Russell et al. 1978）：
公式中i和j指示同位素質(zhì)量數(shù)，Rm和RT分別代表樣品的測(cè)試比值和參考比值（推薦值），f指儀器質(zhì)量分餾因子。205Tl/203Tl被用于計(jì)算Pb的質(zhì)量分餾因子（2.38714，NIST SRM 997證書值）。由于Tl的分餾行為與Pb分餾行為存在一定差別，因此NIST 981被用作外標(biāo)對(duì)數(shù)據(jù)進(jìn)行二次校正。實(shí)驗(yàn)流程采用兩個(gè)Pb同位素標(biāo)樣（NIST 981和AlfaPb）之間插入7個(gè)樣品進(jìn)行分析。全部分析數(shù)據(jù)采用專業(yè)同位素?cái)?shù)據(jù)處理軟件“Iso-Compass”進(jìn)行數(shù)據(jù)處理（Zhang et al., 2020）。NIST 981的20xPb/204Pb的外部測(cè)試精度達(dá)到0.03%（2RSD）。NIST 981的推薦值采用208Pb/204Pb=36.7262±31，207Pb/204Pb=15.5000±13，206Pb/204Pb=16.9416±13（n=119，Baker et al. 2004）。
BCR-2（玄武巖）被選擇作為流程監(jiān)控標(biāo)樣。BCR-2的20xPb/204Pb分析測(cè)試值為208Pb/204Pb=38.736±17，207Pb/204Pb=15.628±3，206Pb/204Pb=18.756±10 （2SD, n=22），與推薦值208Pb/204Pb=38.725±22，207Pb/204Pb=15.621±4，206Pb/204Pb=18.753±8（Zhang and Hu 2020）在0.03%誤差范圍內(nèi)一致。數(shù)據(jù)表明，本實(shí)驗(yàn)流程可以對(duì)樣品進(jìn)行有效分離，分析準(zhǔn)確度和精密度滿足高精度的Pb同位素分析。
本測(cè)試方法適用Pb含量>2ppm的巖石樣品，保證樣品20xPb/204Pb測(cè)試內(nèi)精度（2RSE）0.002%~0.025%），測(cè)試準(zhǔn)確度優(yōu)于0.03%。Pb含量低于2ppm的巖石樣品，測(cè)試精度和準(zhǔn)確度會(huì)受到影響，影響程度受樣品Pb含量控制。低Pb樣品分析請(qǐng)事先咨詢技術(shù)人員，確保樣品分析質(zhì)量。
12.2 Scheme for Pb 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 1.0 mL of 1.0 M HBr. Column chemistry: After centrifugation, the supernatant solution was loaded into an ion-exchange column packed with AG resin. After complete draining of the sample solution, columns were rinsed with 1.0 M HBr to remove undesirable matrix elements. Finally, the Pb fraction was eluted using 6.0 M HCl and gently evaporated to dryness prior to mass-spectrometric measurement.
Pb 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 to monitor 204(Pb+Hg）、206Pb、207Pb、208Pb、203Tl、205Tl和202Hg. 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. Pb 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 NIST 981 was used regularly for uating the reproducibility and accuracy of the instrument. Typically, the signal intensities of 208Pb+ in NIST 981 were > ~6.0 V. The Pb 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 normalization to a 205Tl/203Tl ratio of 2.38714 (the certified value of NIST SRM 997). All data reduction for the MC-ICP-MS analysis of Hf isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020). Because of the difference of the mass bias behaviors between Pb and Tl, all measured 20xPb/204Pb ratios of unknown samples were normalized to the well-accepted NIST 981 values of 208Pb/204Pb=36.7262±31，207Pb/204Pb=15.5000±13，206Pb/204Pb=16.9416±13（n=119，Baker et al. 2004）. One NIST 981 standard was measured every ten samples analyzed. Analyses of NIST 981 standard yielded external precisions of 0.03% (2RSD) for 20xPb/204Pb ratios. In addition, the USGS reference materials BCR-2 (basalt) yielded results of 208Pb/204Pb=38.736±17, 207Pb/204Pb=15.628±3, 206Pb/204Pb=18.756±10 (2SD, n=22)，respectively, which is identical within error of 0.03% to their published values (Zhang and Hu 2020).
References
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.
Baker, J., Peate, D., Waight, T., Meyzen, C. (2004). Pb isotopic analysis of standards and samples using a 207Pb–204Pb double spike and thallium to correct for mass bias with a double-focusing mc-icp-ms. Chemical Geology, 211(3–4), 275-303
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