測試項(xiàng)目：Ca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(wù)。

送樣要求：

完成標(biāo)準(zhǔn)：前處理在超凈室100級超凈臺內(nèi)進(jìn)行，保證監(jiān)測空白及樣品無污染，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：
14.1Ca同位素比值分析
全巖Ca同位素前處理和測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(zhǔn)確稱取粉末樣品50 mg置于Teflon溶樣彈中；（3）先后依次緩慢加入1 ml高純HNO₃和1 ml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1 ml HNO₃ 并再次蒸干；（6）用10 ml 1 M HNO₃溶解樣品，待上柱分離?；瘜W(xué)分離：移取一份含有40 µg Ca的溶液至PFA材質(zhì)交換柱上，柱中填充250 µl DGA樹脂。用4 M HNO₃淋洗去除基體元素，而接近99%的Ca在高純水淋洗下被洗脫并收集。收集的Ca溶液蒸干后用2 % HNO₃再溶解，制備為10 ppm Ca溶液等待上機(jī)測試。前處理的全流程空白一般小于20 ng，與巨大的Ca溶樣量相比可以忽略不計(jì)。
儀器測試流程：
Ca同位素分析在上譜公司采用美國Thermo Fisher Scientific 公司的MC-ICP-MS（Neptune Plus）完成。Ca同位素的測試在濕法條件下進(jìn)行，使用石英雙氣旋霧室和50 μL min⁻¹流速的自提升微量霧化器進(jìn)樣系統(tǒng)。通過高靈敏度的Jet+X錐組合和大抽力的干泵系統(tǒng)的配合，大大提升了儀器的靈敏度。通常10 ppm的Ca溶液能夠獲取5 V以上的⁴⁴Ca信號。每次進(jìn)樣之前，進(jìn)樣系統(tǒng)都要用5 % HNO₃清洗2-3分鐘，使得⁴⁴Ca信號低于1  mV，避免樣品間的交叉污染。為了消除來自氬化物和氮化物的多原子離子干擾，測試在中分辨模式下進(jìn)行。儀器的同位素質(zhì)量分餾采用樣品-標(biāo)樣插值法（SSB法）進(jìn)行校正。所有的Ca同位素?cái)?shù)據(jù)都采用相對于標(biāo)準(zhǔn)物質(zhì)的千分比值形式報道。我們采用一個Alfa Ca純?nèi)芤鹤鳛槿粘２逯捣y試的參考標(biāo)樣。但是為了能夠更好的與發(fā)表數(shù)據(jù)進(jìn)行比較，所有的Ca同位素結(jié)果都轉(zhuǎn)換為相對于NIST SRM 915a報道。每份樣品溶液報道多次測試的平均值和標(biāo)準(zhǔn)偏差（n≥3）。日常測試中，儀器的精確度和準(zhǔn)確度通過反復(fù)測試內(nèi)部標(biāo)準(zhǔn)溶液Alf Ca來評估。此外，在樣品的前處理階段就引入一個Ca同位素的碳酸鹽標(biāo)準(zhǔn)樣品(NIST SRM 915b)，一個玄武巖標(biāo)樣BHVO-2和海水標(biāo)樣當(dāng)做未知樣品用來監(jiān)控全流程。
對NIST SRM 915a的長期測試結(jié)果為0.001 ± 0.058 ‰ (2SD, n = 155)，表明儀器的測試精度優(yōu)于0.06 ‰ (2SD)。 通過反復(fù)地測試，獲取的NIST SRM 915b，BHVO-2和海水的Ca同位素組成分別為0.35 ± 0.04 ‰ (2SD, n = 9)，0.38 ± 0.04 ‰ (2SD, n = 14) 和0.88 ± 0.03‰ (2SD, n = 5). 這些結(jié)果與前人文獻(xiàn)報道值在誤差范圍內(nèi)一致(Heuser and Eisenhauer 2008; Amini et al., 2009; Feng et al., 2018; Li et al., 2018; Kang et al., 2017)，證明了我們對地質(zhì)樣品Ca同位素分析方法的可靠性。
14.2 Scheme for Ca 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) 10 - 50 mg sample powder was accurately weighed and placed in an Teflon bomb; (3) 1 ml HNO₃ ａnd 1 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 at least 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 10 mL of 4 M HHNO₃. Column chemistry: An aliquot sample solution containing 40 μg Ca was loaded onto the pre-cleaned PFA column which filled with 250 µl DGA resin. All the sample matrices were removed by 4 mol L^-1 HNO₃ while quantitative recovery (>99 %) of Ca was achieved by the elution of MQ-H₂O. The collected Ca fractions were evaporated to dryness and re-dissolved in 2 % HNO₃ to obtain 10 ppm Ca solution prior to MC-ICP-MS analysis. The total procedural blank was no more than 20 ng which is negligible compared to the digestions.
Calcium isotopes analyse 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. A “wet” plasma, using a quartz dual cyclonic-spray chamber and an Savillex 50 μL min⁻¹ PFA MicroFlow Teflon nebulizer (Elemental ScientificInc., U.S.A.), was utilized to measure Ca isotopes. 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. Typically, the signal intensities of ⁴⁴Ca⁺ in 10 ppm sample solution were > 5 V. Cross-contamination between samples was eliminated by washing the sample-introduction system with 5% HNO₃ for 2-3 min between each measurement until the ⁴⁴Ca signal is less than 1 mV. Medium resolution mode was used to resolve polyatomic interference, such as ⁴⁰Ar¹H²⁺ａnd ¹⁴N³⁺. The instrumental drift was corrected by the standard-sample bracketing technique. All the Ca isotopic compositions were reported relative to a reference standard by using δ-notation: δ^44/42Ca_ref = [⁴⁴Ca/⁴²Ca_sample/⁴⁴Ca/⁴²Ca_ref -1] × 1000. An in-house Alfa Ca standard solution (Lot:9192737) was used as bracketing reference standard in our laboratory. However, in order to achieve better comparability of published Ca isotope data, all Ca isotope results were reported relative to commonly used reference standard NIST SRM 915a by adding a conversion factor 0.58 (the δ^44/42Ca_SRM915a value of Alfa Ca). Each sample solution has been measured multiple times (≥3), and the two times standard deviation is reported as the analytical uncertainty. The instrumental precision and accuracy during routine Ca isotope measurements was monitored by intermediate measurements of Alf Ca. A calcium carbonate standard NIST SRM915b, a basalt rock standard BHVO-2 and seawater samples were processed as unknowns to assess accuracy and reproducibility.
The long-term (>3 months) average δ^44/42Ca_SRM915a of NIST 915a is 0.001 ± 0.058 ‰ (2 SD, n = 155) indicated that the reproducibility of our instrument is better than 0.06‰ (2 SD). The repeated analyzed NIST SRM 915b, BHVO-2 and seawater are 0.35 ± 0.04 ‰ (2 SD, n = 9), 0.38 ± 0.04 ‰ (2 SD, n = 14) and 0.88 ± 0.03‰ (2 SD, n = 5). These results are consistent with previous studies within analytical uncertainty, conforming the accuracy of our analytical method for Ca isotopes in geological samples (Heuser and Eisenhauer 2008; Amini et al., 2009; Feng et al., 2018; Li et al., 2018; Kang et al., 2017). 
References
Heuser A. and Eisenhauer A. (2008). The Calcium Isotope Composition (δ^44/40Ca) of NIST SRM 915b and NIST SRM 1486 Geostandards and Geoanalytical Research, 32, 311-315.
Amini M., Eisenhauer A., Böhm F., Holmden C., Kreissig K., Hauff F. and Jochum K.P. (2009). Calcium Isotopes (δ^44/40Ca) in MPI-DING Reference Glasses, USGS Rock Powders and Various Rocks: Evidence for Ca Isotope Fractionation in Terrestrial Silicates Geostandards and Geoanalytical Research, 33, 231-247.
Feng L., Zhou L., Yang L., Zhang W., Wang Q., Tong S. and Hu Z. (2018). A rapid and simple single-stage method for Ca separation from geological and biological samples for isotopic analysis by MC-ICP-MS Journal of Analytical Atomic Spectrometry, 33, 413-421.
Li M., Lei Y., Feng L., Wang Z., Belshaw N.S., Hu Z., Liu Y., Zhou L., Chen H. and Chai X. (2018). High-precision Ca isotopic measurement using a large geometry high resolution MC-ICP-MS with a dummy bucket Journal of Analytical Atomic Spectrometry, 33, 1707-1719.