測(cè)試項(xiàng)目：Nd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：

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：
11.1全巖Nd同位素比值分析
全巖Nd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：
化學(xué)分離：通過Sr分離流程獲得的REE溶液經(jīng)過介質(zhì)轉(zhuǎn)換后，直接上柱分離。柱子填充LN樹脂。用0.18M HCl淋洗去除基體元素。最終用0.3M HCl將Nd從柱上洗脫并收集。收集的Nd溶液蒸干后等待上機(jī)測(cè)試。
儀器測(cè)試流程：
Nd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。¹⁴²Nd⁺、¹⁴³Nd⁺、¹⁴⁴Nd⁺、¹⁴⁵Nd⁺、¹⁴⁶Nd⁺、¹⁴⁷Sm⁺、¹⁴⁸Nd⁺、¹⁴⁹Sm⁺、¹⁵⁰Nd⁺同時(shí)被L4、L3、L2、L1、C、H1、H2、H3、H4等9個(gè)接收器接收。其中¹⁴⁷Sm⁺被用于監(jiān)控并校正Sm對(duì)Nd同位素的同質(zhì)異位素干擾。MC-ICP-MS采用了H+S錐組合和干泵以提高儀器靈敏度。根據(jù)樣品中的Nd含量，50 µl/min-100 µl/min兩種微量霧化器被選擇使用。Alfa公司的Nd單元素溶液被用于優(yōu)化儀器操作參數(shù)。Nd標(biāo)準(zhǔn)物質(zhì)（GSB 04-3258-2015，200 µg/L）的¹⁴²Nd信號(hào)一般高于2.5 V。數(shù)據(jù)采集由10個(gè)blocks組成，每個(gè)block含8個(gè)cycles，每個(gè)cycle為4.194秒。Nd同位素的儀器質(zhì)量分餾采用內(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)，R_m和R_T分別代表樣品的測(cè)試比值和參考值（推薦值），f指儀器質(zhì)量分餾因子。¹⁴⁶Nd /¹⁴⁴Nd被用于計(jì)算Nd的質(zhì)量分餾因子（0.7219，Lin et al. 2016）。由于前期有效的樣品分離富集處理，干擾元素Sm被分離干凈。殘留的¹⁴⁴Sm⁺干擾校正采用Lin et al.（2016）校正方法。實(shí)驗(yàn)流程采用兩個(gè)Nd同位素標(biāo)樣（GSB 04-3258-2015 和AlfaNd）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）。GSB 04-3258-2015的¹⁴³Nd /¹⁴⁴Nd分析測(cè)試值為0.512440±6（2SD, n=31）與推薦值0.512438±6（2SD）（Li et al., 2017）在誤差范圍內(nèi)一致，表明本儀器的穩(wěn)定性和校正策略的可靠性滿足高精度的Nd同位素分析。
BCR-2（玄武巖）和RGM-2（流紋巖）（USGS）被選擇作為流程監(jiān)控標(biāo)樣。兩個(gè)樣品分別代表了基性巖和酸性巖，具有顯著的物理化學(xué)差異。BCR-2和RGM-2具有適中的Nd含量（28.7 µg/g和19 µg/g）。BCR-2的¹⁴³Nd /¹⁴⁴Nd分析測(cè)試值為0.512641±11（2SD, n=82），與推薦值0.512638±15（Wei et al. 2006）在誤差范圍內(nèi)一致。RGM-2的¹⁴³Nd /¹⁴⁴Nd分析測(cè)試值為0.512804±12（2SD, n=80），與推薦值0.512803±10（Li et al. 2012）在誤差范圍內(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Nd同位素分析。
本測(cè)試方法適用Nd含量>3 ppm的巖石樣品，保證實(shí)際地質(zhì)樣品測(cè)試內(nèi)精度（2SE）=0.000005-0.000025（0.01‰~0.05‰，2RSE），測(cè)試準(zhǔn)確度優(yōu)于0.000025（~0.05‰），視樣品Nd含量而定。Nd含量低于3 ppm的巖石樣品，測(cè)試內(nèi)精度和準(zhǔn)確度會(huì)受到影響，影響程度受樣品Nd含量控制。低Nd樣品分析請(qǐng)事先咨詢技術(shù)人員，確保樣品分析質(zhì)量。
11.2 Scheme for Nd 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. Column chemistry: The REE solution from the Sr-column method was evaporated to incipient dryness, and taken up with 0.18 M HCl. The converted REE solution was loaded into an ion-exchange column packed with LN resin. After complete draining of the sample solution, columns were rinsed with 0.18 M HCl to remove undesirable matrix elements. Finally, the Nd fraction was eluted using 0.3 M HCl and gently evaporated to dryness prior to mass-spectrometric measurement.
Nd 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 ¹⁴²Nd⁺、¹⁴³Nd⁺、¹⁴⁴Nd⁺、¹⁴⁵Nd⁺、¹⁴⁶Nd⁺、¹⁴⁷Sm⁺、¹⁴⁸Nd⁺、¹⁴⁹Sm⁺、¹⁵⁰Nd⁺. The large dry interface pump (120 m³ hr^-1 pumping speed) and newly designed H skimmer cone and  the standard sample cone were used to increase the instrumental sensitivity. Nd single element solution from Alfa (Alfa Aesar, Karlsruhe, Germany) was used to optimize instrument operating parameters. An aliquot of the standard solution of 200 μg L⁻¹ GSB 04-3258-2015 was used regularly for uating the reproducibility and accuracy of the instrument. Typically, the signal intensities of ¹⁴²Nd⁺ in GSB 04-3258-2015 were > ~2.5 V. The Nd 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 ¹⁴⁶Nd /¹⁴⁴Nd ratio of 0.7219 (Lin et al. 2016). The interference elements Sm have been completely separated by the exchange resin process. The remaining interferences of ¹⁴⁴Sm⁺ were corrected based on the mothed described by Lin et al. (2016). All data reduction for the MC-ICP-MS analysis of Nd isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020). One GSB 04-3258-2015 standard was measured every seven samples analyzed. Analyses of the GSB 04-3258-2015 standard yielded ¹⁴³Nd /¹⁴⁴Nd ratio of 0.512440±6（2SD, n=31）, which is identical within error to their published values (0.512438±6（2SD）Li et al., 2017). In addition, the USGS reference materials BCR-2 (basalt) and RGM-2 (rhyolite) yielded results of 0.512641±11（2SD, n=82） ａnd 0.512804±12（2SD, n=80） for ¹⁴³Nd/¹⁴⁴Nd, respectively, which is identical within error to their published values (Wei et al. 2006；Li et al. 2012).
References
Li, C. F., Li, X. H., Li, Q. L., Guo, J. H., & Yang, Y. H. (2012). Rapid and precise determination of sr and nd isotopic ratios in geological samples from the same filament loading by thermal ionization mass spectrometry employing a single-step separation scheme. Analytica Chimica Acta, 727 (10), 54-60.
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., 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.
Jin Li., Suo-han Tang., Xiang-kun Zhu., Chen-xu Pan. (2017). Production and Certification of the Reference MaterialGSB 04-3258-2015 as a 143Nd/144Nd Isotope Ratio Reference. Geostand. Geoanal. Res., 2017, 41, 255-262.